So,
All you have to do is to translate the words into open sentences with placeholders.
Apparently, there are 2 numbers, call them x and y.
Now, build open sentences.
x + y = 12
x - y = 4
Now, which method will we use to solve? I choose Elimination by Addition.
Add the equations together.
2x = 16
Divide both sides by 2
x = 8
Substitute
8 + y = 12
Subtract 8 from both sides.
y = 4
Check
The sum of the two numbers is 12 (8 + 4).
The difference of the two numbers is 4 (8 - 4).
The first number is 8.
The second number is 4.
