#pragma comment(linker, "/STACK:1024000000,1024000000")

#include <cstdio>

#include <string>

#include <cstdlib>

#include <cmath>

#include <iostream>

#include <cstring>

#include <set>

#include <queue>

#include <algorithm>

#include <vector>

#include <map>

#include <cctype>

#include <cmath>

#include <stack>

//#include <tr1/unordered_map>

#define freopenr freopen("in.txt", "r", stdin)

#define freopenw freopen("out.txt", "w", stdout)

using namespace std;

//using namespace std :: tr1;

typedef long long LL;

typedef pair<int, int> P;

const int INF = 0x3f3f3f3f;

const double inf = 0x3f3f3f3f3f3f;

const LL LNF = 0x3f3f3f3f3f3f;

const double PI = acos(-1.0);

const double eps = 1e-8;

const int maxn = 1e3 + 5;

const LL mod = 10000000000007;

const int N = 1e6 + 5;

const int dr[] = {-1, 0, 1, 0, 1, 1, -1, -1};

const int dc[] = {0, 1, 0, -1, 1, -1, 1, -1};

const char *Hex[] = {"0000", "0001", "0010", "0011", "0100", "0101", "0110", "0111", "1000", "1001", "1010", "1011", "1100", "1101", "1110", "1111"};

inline LL gcd(LL a, LL b){  return b == 0 ? a : gcd(b, a%b); }

int n, m;

const int mon[] = {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};

const int monn[] = {0, 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};

inline int Min(int a, int b){ return a < b ? a : b; }

inline int Max(int a, int b){ return a > b ? a : b; }

inline LL Min(LL a, LL b){ return a < b ? a : b; }

inline LL Max(LL a, LL b){ return a > b ? a : b; }

inline bool is_in(int r, int c){

    return r >= 0 && r < n && c >= 0 && c < m;

}

struct Point{

    double x, y;

};

struct Edge{

    int to, next;

};

Edge edge[maxn<<1];

Point a[maxn];

double dist[maxn][maxn], lowc[maxn], dp[maxn][maxn];

bool vis[maxn], is_tree[maxn][maxn];

int pre[maxn], head[maxn];

int cnt;

double sum, ans;

double Distan(const Point& lhs, const Point& rhs){

    return sqrt((lhs.x - rhs.x) * (lhs.x - rhs.x) + (lhs.y - rhs.y) * (lhs.y - rhs.y));

}

void add(int u, int v){

    edge[cnt].to = v;

    edge[cnt].next = head[u];

    head[u] = cnt++;

}

void Prim(){

    sum = 0.0;

    memset(vis, false, sizeof vis);

    memset(pre, 0, sizeof pre);

    for(int i = 1; i < n; ++i)  lowc[i] = dist[0][i];

    vis[0] = true;

    for(int i = 1; i < n; ++i){

        double minc = inf;

        int p = -1;

        for(int j = 0; j < n; ++j)

            if(!vis[j] && minc > lowc[j]) minc = lowc[j], p = j;

        sum += minc;

        vis[p] = true;

        add(p, pre[p]);

        add(pre[p], p);

        for(int j = 0; j < n; ++j)

            if(!vis[j] && lowc[j] > dist[p][j])

                lowc[j] = dist[p][j], pre[j] = p;

    }

}

double dfs(int u, int fa, int root){

    double ans = fa == root ? inf : dist[root][u];

    for(int i = head[u]; ~i; i = edge[i].next){

        int v = edge[i].to;

        if(v == fa)  continue;

        double tmp = dfs(v, u, root);

        ans = min(ans, tmp);

        dp[u][v] = dp[v][u] = min(dp[u][v], tmp);

    }

    return ans;

}

void dfs1(int u, int fa){

    for(int i = head[u]; ~i; i = edge[i].next){

        int v = edge[i].to;

        if(v == fa)  continue;

        if(fa)  ans = max(ans, sum-dist[u][v]+dp[u][v]);

        dfs1(v, u);

    }

}

int main(){

    int T;  cin >> T;

    while(T--){

        scanf("%d %d", &n, &m);

        for(int i = 0; i < n; ++i)  scanf("%lf %lf", &a[i].x, &a[i].y);

        for(int i = 0; i < n; ++i)

            for(int j = i+1; j < n; ++j)

                dist[i][j] = dist[j][i] = Distan(a[i], a[j]);

        cnt = 0;

        memset(head, -1, sizeof head);

        Prim();

        for(int i = 0; i < n; ++i)

            for(int j = 0; j < n; ++j)  dp[i][j] = inf;

        for(int i = 0; i < n; ++i)  dfs(i, -1, i);

        ans = sum;

        dfs1(0, 0);

        ans *= m * 1.0;

        printf("%.2f\n", ans);

    }

    return 0;

}