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A. v = r*w where v is the outer velocity (50 mi/hr) and r is the radius (48 in)
Doing a few conversions, we get that 50 mi/hr = 52800 in/min
w = v/r = (52800 in/min)/(48 in) = 1100 rad/min
B. 1 rev = 2pi rad so do a unit conversion
(1100 rad/min)*(1 rev / 2pi rad) = 175.07 rpm