Answer:

Explanation:
Case 1
Given,
initial angular speed = 0 rev/s
final angular speed = 2 rev/s
time, t = 7 s
angular acceleration of the washer



using equation of rotational motion



Case 2
Given,
initial angular speed = 2 rev/s
final angular speed = 0 rev/s
time, t = 12 s
angular acceleration of the washer



using equation of rotational motion



total revolution in this case



total revolution of the washer is equal to 20 rev.