You and your friend have been walking for a total of 15 minutes on two different streets. You are walking 4 feet per minute and your friend is walking 6 feet per minute for a total of 72 feet. Write a system of linear equations to represent this situation.

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)