The position of an object as a function of time is given by
x(t)=at^3-bt^2+ct-d , where a=2.2m/s^3 b=5.8m/s^2 c=6m/s and d=7m

(a) Find the instantaneous acceleration at t= 4.9 s.
(b) Find the average acceleration over the first 4.9 seconds.