Let me state an example:
There are two consecutive even numbers. The sum of the two consecutive even numbers is 20. If the difference of the two numbers is 2, find the numbers.
Let:
x-be first number
x+2-second number
x+y=20
x-y=2
We can pick any equation and find the value of either of the variables, but I will select the second equation instead.
x-y=2
x=y+2
x+y=20
since the value of x is y+2, substitute the value.
y+2+y=20
2y+2=20
2y=18
y=9
Substitute the value of y in the value of x
x=y+2
x=9+2
x=11.
Hope this helps =)
