Could you please show me the clear and specific steps and answer to solve this question below?

Thank you so much :) - the acceleration when the particle is at rest

A particle moves back and forth along a straight line. Its position (in meters), relative to the origin, at any time t (in seconds) is given by s(t) = 3+3 - 9t2 + 5t - 15. Find: (remember to include units) $ 200: the acceleration when the particle is at rest