A disk of radius 10 cm speeds up from rest. It turns 60 radians reaching an angular velocity of 15 rad/s. What was the angular acceleration? B.How long did it take the disk to reach this velocity?

a=w^2/2(theta)
a=15^2/(2(60))
a=1.875 rad/s^2
t=w/a
t=15/1.875
t=8 s
Is this correct if not correct me.