On two examinations, you have grades of 86 and 88. There is an optional final

Chapter 6, Problem 87

(choose chapter or problem)

On two examinations, you have grades of 86 and 88. There
is an optional final examination, which counts as one grade.
You decide to take the final in order to get a course grade of
A, meaning a final average of at least 90.
a. What must you get on the final to earn an A in the
course?
b. By taking the final, if you do poorly, you might risk the B
that you have in the course based on the first two exam
grades. If your final average is less than 80, you will lose
your B in the course. Describe the grades on the final
that will cause this to happen.