Easton and harper are at the pool. harper dives in and touches the bottom of the pool, 15 feet below the surface of the water. easton is standing on the diving board 4 feet above the surface. what is the vertical distance between harpers hand and easton's feet

The position of a moving particle is given by the position function: f(t)=-9t-t^2-0.2t^3+0.1t^4 0 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)