Answer:
x = 6, y = 3
Explanation:
Let Sally's age be x and Tomas's age be y.
Sum of Sally's age plus twice Tomas's age: x + 2y = 12
Difference of Sally's age and Tomas's age: x - y = 3
Multiply the second equation by two and add it to the first equation to get
3x = 18, which means x = 6.
Plug 6 in for x in the second equation to get 6 - y = 3, which means y = 3.