A capstan on a magnetic tape drive rotates at 3600 rad/min and drives the tape at a speed of 45.0 m/min. Find the diameter of the capstan in millimeters

arc length = tape length

s = rθ
ds/dt = r dθ/dt

45m/min = r * 3600/min
45m/3600 = r
r = 45000mm/3600
r = 12.5 mm