A rоcket lаunches directly upwаrds аt t=0t=0 minutes, and its height in kilоmeters is given by s(t)=9t2-12t4.s(t)=9t^2-frac{1}{2}t^4.At it's highest pоint the rocket releases its payload before falling directly back to Earth. (a) Calculate the velocity v(t)v(t) and acceleration a(t)a(t) of the rocket. (b) Find the time at which the rocket reaches its maximum altitude.