The tub of a washer goes into it’s spin-dry cycle, starting from rest and reaching an angular speed of 6.0 rev/s in 9.0 s. At this point, the person doing the laundry opens the lid, and a safety switch turns off the washer. The tub slows to rest in 9.0 s. During how many revolutions does the tub turn through this 18 s interval? Assume constant angular acceleration while it is starting and stopping.