Convert 90 mins to hours full working plz

Ineed with this problem 21 show steps

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%)

Using the rise/run counting method, the slope of the line is