Maria's test scores are 80, 70, and 90. What score does she need to get on a fourth test so that her average score for the four tests is exactly 85? Let's answer step by step:
She needs to have a total of 4 * 85 = 340 points over the four tests. She has 80 + 70 + 90 = 240 points so far. She needs 340 - 240 = 100 on the fourth test. The answer: 100.