A particle P starts from rest at a point O of a straight line and moves along the line. The displacement of the particle at time t s after leaving O is x m, where

\(x = 0.08t^2 - 0.0002t^3\).

1. Find the value of t when P returns to O and find the speed of P as it passes through O on its return.
2. For the motion of P until the instant it returns to O, find
   1. the total distance travelled,
   2. the average speed.