Let's say that Maria had 270 as a total score, which is true. The problem is asking for an addition problem to help determine the second score Maria might have gotten.
In order to solve this, you need an equation. Knowing the rules of addition and subtraction, you put 92 and 88 together, and get a sum of 180.
92 + 88 is your addition problem in this question
Now, in order to find the difference, or the second score, you need to subtract.
All you need to do is do a simple equation ↓↓ ↓↓ 270 (total of all scores including the second one) - 180 (the sum of the addition equation) = 90