Let be the mean (in points) of four test scores, x1, x2, x3, and x4, all

Question:

Let be the mean (in points) of four test scores, x1, x2, x3, and x4, all in points.
a. Write a formula for the mean of the test scores.
b. Solve the formula you found in part (a) for x4.
c. If a student has test scores of 85, 93, and 89, all in points, use the formula you found in part (b) to find the score she needs on the fourth test so that her four-test mean is 90 points, which is the cutoff for an A.