An architect is designing a new library. As shown, the library's floor plan is a rectangle divided into a
bookshelf space with bookshelves, and a reading space with a rug and chairs. Each bookshelf is x ft
wide and x + 3 ft long. The bookshelves are 3 ft from each other. The walkway between the two rows
of bookshelves is 2 ft wide.

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)