I need help! Question is in attachment.

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%)

Find the interior angle of a regular polygon which has 6 sides

Abari owns 100 shares of stock a and 45 shares of stock b. for the past month, his stocks have been fluctuating inversely. stock a decreased by m cents per share and stock b increased by n cents per share. which equation can be used to find the total change in value of jabari's shares per month?