Answer:
It takes his friend 24 hours
Step-by-step explanation:
The formula for time on a job is
1/A + 1/B = 1/C
where A is the time for person A
B is the time for person B
C is the time for A and B together
Tom is person A and his friend is person B
1/12 + 1/B = 1/8
The Common denominator is 24, so multiply by 24 on each side
24(1/12 + 1/B) = 1/8*24
2 +24/B = 3
Subtract 2 from each side
2-2 +24/B = 3-2
24/B =1
Multiply each side by B
24/B *B = B*1
24 = B
