Final answer:
To have a 90 average in the class, you need to score 102 on the 5th test.
Step-by-step explanation:
To find out what score you need on the 5th test to have a 90 average in the class, you need to calculate the average of all 5 test scores. The average is found by summing up all the test scores and dividing by the number of tests. In this case, the sum of the first 4 test scores is 85 + 80 + 90 + 93 = 348. To have a 90 average, the sum of all 5 test scores should be (90 * 5) = 450. Subtracting the sum of the first 4 test scores from 450, we get the score you need on the 5th test: 450 - 348 = 102.