Sani's course grade in his chemistry class is based on
3 tests and 1 final exam. Each of the 3 test scores is
weighted as 20% of the course grade, and the final
exam score is weighted as 40% of the course grade.
Sani's 3 test scores are 78, 86, and 82, respectively.
What is the minimum score that Sani will have to earn
on the final exam in order to receive a course grade of
at least 86 ?