Answer
given,
cooling fan revolution = 850 rev/min
fan turns before revolution = 1500 revolutions


θ = 1500 revolution
θ = 1500 x 2 x π
θ = 9424.78 rad
a) using equation of rotation
ω² = ω₀² + 2 α θ
ω = 0 because body comes to rest
0 = 89² + 2 x α x 9424.78
α = -0.42 rad/s²
b) time take for the fan to stop
ω = ω₀ + α t
0 = 89 - 0.42 t

t = 211.9 s
The correct answer for this question is 6m/s. I hope this helps.
The answer to the question '<span>In a series of undisturbed rock layers where shale lies between sandstone below and limestone above, the __." would be limestone is youngest. Out of all the rock layers, the limestone is dated to be the youngest of all.</span>
the answer is the forth one treatment of cancer