Which equation of c makes this equation true. 12-9+c =12 Pls only direct answers

Can someone me with these two circle theorem questions asap?

Combine the information in the problem and the chart using the average balance method to solve the problem.

The position of a moving particle is given by the position function: f(t)=-9t-t^2-0.2t^3+0.1t^4 a. at what time does the particle reverse direction? b. when is the displacement positive? (round one decimal place and answer in interval notation) c. when is the displacement negative? (round one decimal place and answer in interval notation) d. when is the particle’s acceleration positive? (round one decimal place and answer in interval notation) e. when is the particle’s acceleration negative? (round one decimal place and answer in interval notation)