Answer part a, using derivatives, show all steps, including algebra steps

13. s(t) = 2t4 - 8+3 + 8t2 + 1 is the position function of a body moving along a coordinate line, where t 2 0, and s(t) is measured in feet and t in seconds. a. Determine the times when the body is stationary. b. When is the body moving in the positive direction