This is really making my head hurt. i don't understand it at all. if i get this one wrong, and all the other three like this, i'm gonna fail my test.
can you figure out number 8 and show how you got it?

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)

A25- foot ladder leans against a building and reaches a point of 23.5 feet above the ground .find the angle that the ladder makes with the building

Given sin28.4=.4756, cos28.4=.8796, and tan28.4=.5407 find the cos of 61.6