You need to use 4/5 cups of strawberries for a single pie how many cups are needed for 2 pies i know the answer is 13/5 but how do you work that out

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%)