Question

The sum of two numbers is 15.

Answer 1

X + y = 15
x - y =3

First you have to work out what two numbers add together to make 15, for example 1 and 14 or 5 and 10. 
Then you have to work out which set of numbers have a difference of 3.
The numbers would be 6 and 9.

Once you have the two numbers, multiply them together:
6 x 9 = 54