Answer:
98
Step-by-step explanation:
Average is the sum of all data points divided the number of data points.
In this specific situation, the average test score, 91, is equal to the sum of Molly's four individual test scores divided by the number of test Molly had, 4.
(( 86 + 87 + 93 + x) / 4) = 91
86 + 87 + 93 + x = 91/4
86 + 87 + 93 + x = 364
x = 364 - 93 - 87 - 86 = 98
