#include <stdio.h>

 #include <string.h>

 #include <math.h>

 #include <algorithm>

 #include <iostream>

 #include <ctype.h>

 #include <iomanip>

 #include <queue>

 #include <stdlib.h>

 using namespace std;

 #define INF 0x3fffffff

 int f[];

 int n,m;

 struct lu

 {

     int start,end,speed;

 }num[];

 bool cmp(lu a,lu b)

 {

     return a.speed > b.speed;

 }

 int gcd(int a, int b)

 {

     while(b != )

     {

         int r = a % b;

         a = b;

         b = r;

     }

     return a;

 } 

 void init(int n)

 {

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

         f[i]=i;

 }

 int find(int x)

 {

     if(x==f[x])

         return f[x];

     f[x]=find(f[x]);

     return f[x];

 }

 void Union(int x,int y)

 {

     int p=find(x);

     int q=find(y);

     if(p > q)

         f[p] = q;

     else

         f[q] = p;

 }

 int main()

 {

     int t;

     int a,b,i,j,aa,bb;

     scanf("%d",&t);

     while(t--){

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

         for(i=;i<m;i++)

             scanf("%d %d %d",&num[i].start,&num[i].end,&num[i].speed);

         sort(num,num+m,cmp);

         scanf("%d %d",&a,&b);

         double rate = INF*1.0;

         for(i=;i<m;i++){

             init(n);

             for(j=i;j<m;j++){

                 if(find(num[j].start)!=find(num[j].end))

                     Union(num[j].start,num[j].end);

                 if(find(a)==find(b))

                     break;

             }

             if(j==m) break;

             int v1=num[i].speed,v2=num[j].speed;

             if(v1*1.0 / v2 < rate){

                 aa=v1,bb=v2;

                 rate=v1*1.0 / v2;

             }

         }

         if(rate == INF)

             printf("IMPOSSIBLE\n");

         else if(aa % bb == )

             printf("%d\n",aa/bb);

         else

             printf("%d/%d\n",aa/ gcd(aa,bb),bb/ gcd(aa,bb));

     }

 }