A disk rotates about its central axis starting from rest and accelerates with constant angular acceleration. At one time it is rotating at 9.80 rev/s; 80.0 revolutions later, its angular speed is 18.0 rev/s. Calculate (a) the angular acceleration (rev/s2), (b) the time required to complete the 80.0 revolutions, (c) the time required to reach the 9.80 rev/s angular speed, and (d) the number of revolutions from rest until the time the disk reaches the 9.80 rev/s angular speed.