Question

The sum of two numbers is 30 & their difference is 12.

Answer 1

The answer is 21 and 9. You can use guess and check to solve this. If you add 21 and 9, the sum is 30, and if you subtract 9 from 21, the difference is 12. 

Answer 2

x+y=30
x-y=12
add them together

x+y=30
x-y=12+
2x+0y=42

2x=42
divide 2
x=21

subsitute
x+y=30
21+y=30
subtrat 21
y=9


number sare 21 and 9