Can someone please do this for me! I have been trying to do it for days and can’t figure it out!!

What you have to do find the length of the missing side of the pink triangle on the top, but you have to use all of the other triangles to do so.
PLEASE SHOW YOUR WORK!

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)