ANSWER
Option D
EXPLANATION
The word problem is:
A student has two grades of 80 and 90. What grade must the students make on the next test to pass the class with a 90 grade average?
The problem tells us that the average of the three grades is 90.
This means that if we add the three grades and divide by 3, we should get 90.
Let the missing grade be x.
This means that:
(80 + 90 + x) / 3 = 90
That is the answer.