The sum of two numbers is 12. if one number is subtracted from the other, their difference is -2. find the numbers

The first number is 5
the 2nd number is 7

We can solve this by setting up a system of equations. x and y will represent the two numbers.
x+y = 12
x-y = -2
Personally, I'm going to solve the system by solving one of the equations for x and substituting it into the other one.
x = 12-y
12-y-y = -2
12-2y = -2
-2y = -14
y = 7

Now find the other number by plugging 7 in for y in one of the equations.
x+7 = 12
x = 5
OR
x-7 = -2
x = 5

So, the two numbers are 5 and 7.