Question

a and b can do a job in 12 days,after working for 2 days,they are assisted by c,who works at the same rate as a. the work takes 6 1/4 days more to finish. in how many days will b alone do the work?

Answer 1

According to question

1/a + 1/b = 1/12
and 
also       1/a + 1/b + 1/c = 1/10 + 25/4  = 4/73
Thus putting the values we get

1/12 + 1/c = 4/73
       1/c = 1/12 - 4/73
       1/c = 25/ 876

Answer 2

I hope that it will helps you.