Please help me, solve for n

Describe the 2 algebraic methods you can use to find the zeros of the function f(t)=-16t^2+400.

1) you deposit $2,500 in an account that earns 4% simple interest. how much do you earn in eight years?

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%)