sum = 0

 with open('a.txt',mode='w',encoding='utf-8') as f:

     f.write('''apple 10 3

 tasla 100000 1

 mac 3000 2

 lenove 30000 3

 chicken 10 3''')

 with open('a.txt',encoding='utf-8') as read_f:

     for line in read_f.readlines():

         sum += int(line.split(' ')[1])*int(line.split(' ')[2])

 print(sum)

 import os

 with open('a.txt',mode='w',encoding='utf-8') as f:

     f.write('''alex 18

 Eva 20

 KID 21

 kidd 22

 alex 38''')

 with open('a.txt',encoding='utf-8') as read_f,\

     open('aa.txt',mode='w',encoding='utf-8') as write_f:

     for line in read_f.readlines():

         line = line.replace('alex','SB')

         write_f.write(line)

 os.remove('a.txt')

 os.rename('aa.txt','a.txt')