Probably the easiest way is to find the average velocity = (1/t) integral from 0 to t of a(t')dt' + v0
In this case, v avg (t) = (1/t)(19.1t2/2 - t3/3) (0 limit is 0 when you plug it in and v0 = 0) = 9.55t - t2/3
d = vavg(t) t = vavg(8.8s)(8.8s)
Please consider a tutor. Take care.
The usual way is to use v-v(0) = integral from 0 to t of adt and then d = integral from 0 to t of vdt.