Answer:
24 hours
Explanation:
The formula is
1/a + 1/b = 1/c where a and b are the times alone and c is the times together
1/12 + 1/b = 1/8
Multiply by 24b to clear the fractions
24b(1/12 + 1/b = 1/8)
2b + 24 = 3b
Subtract 2b from each side
2b +24-2b = 3b-2b
24 = b