Unit rates 12 cans for 6 people

Ill mark the brainliest if you me with the these three questions 7,8,9

There are 45 questions on your math exam. you answered 810 of them correctly. how many questions did you answer correctly?

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%)