If Mina has 35 whole cookies then subtracted 7/2 how much does he have let Help me I mean I have the answer because I memorize it but I can't remember the steps plz help O>O I forget easily T^T

Astudent must have an average on five test that is greater than it equal to 80% but less than 90% to receive a final grade of b. devon's greades on the first four test were 78% 62% 91% and 80% what range if grades on the fifth test would give him a b in the course? ( assuming the highest grade is 100%)