Question

So far this semester, Zachary has test scores of 92, 98, 65, 77, 91, and 85. He has one more test to take before the semester ends. What must he score on the last test to earn an average of 85 for the semester? Type a numerical answer in the space provided.

Answer 1

He has to at least make an 87

Answer 2

Et X be the last test. 
Therefore, 
85=(92+98+65 +77+91+85+X) / 7 
Solving this equation^, 
we get X=87.