I'm not really good at math, but i would appreciate it if i can get some help with this math problem. 2y^3-4x^2-4-1+3x^2-3y^3-y^3

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%)