Write an equation in point slope form for the given point and slope point (4 -6) slope 2 pleasee help ill give you 50 points if u help me and give me the right answer

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%)