To find an average, you simply add up all of your numbers and then divided by the number of numbers you added.
I explained that poorly, so I'll show you how to do it.
So we have 92, 95, 88, and 83. We need to add these together.
(We can just use a calculator)
92 + 95 + 88 + 83 = 358.
We're already halfway done!
Now because there were 4 numbers that we were adding together, we have to divide that number by 4.
(Again just use a calculator if you're lazy)
358 / 4 = 89.5.
So Maggie's average score (Or mean score, as it's also called) is 89.5.
Hope this helps!