Ais 5 yrs older that b. the product of their ages is 84. how old is each?

84 =

1 * 84 = 84
2 * 42 = 84
3 * 28 = 84
4 * 21 = 84
6 * 14 = 84
7 * 12 = 84

If the first number was B, and the second number was A, you'd just need to find which two numbers show that A is 5 more than B.

The only pair that do this is 7 and 12, because is if A is 12 and B is 7, you can work out that A = 7 + 5, which is 12, so it works. 

A = 12
B = 7