Physic Question help

A flywheel has angular acceleration a(t)= 8.50 rad/s^2 - (2.45 rad/s^2)t, where counterclockwise rotation is positive.
a) If the flywheel is at rest at t=0, what is its angular velocity at 6.00s?

b) Through what angle (in radians) does the flywheel turn in the time interval from t=0 to 6.00s?

for a) I took the integral of a(t) from 0 to 6.00 and got (w)= 6.90 rad/s

for b) since it's 6.90 rad per seconds, I multiply that by 6.00 and got 41.4 rad, and it's wrong. :( , please help!
This is the last question out of 43 questions and it's due in 2 days!!! please help.

You already integrated acceleration to find the velocity. You need to integrate one more time to get angular displacement:
a(t) = 8.5 - 2.45t
ω(t) = 8.5t - 1.225t²
θ(t) = 4.25t² - 0.408t³