A scooter starts from rest and its velocity rises uniformly to 15m/s in 3s. It then maintains this velocity for the next 2s and finally slows down uniformly to 5m/s in the last 1s. Find the average acceleration of the scooter over the entire 6s interval.
(a) 2.50m/s2
(b) 0.83m/s2
(c) −1.67m/s2
(d) 1.67m/s2