Can someone explain how to do this and the answer?

Me with this one question, and i'll upvote the brainliest answer

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

Which of the following would be a reasonable estimate for the weight of a pencil? a. 1 × 10^-20 lb b. 1 × 10^20 lb c. 1 × 10^2 lb d. 1 × 10^-2 lb