Verified answer

feet per minute is a speed rating where a foot is 12 inches or 30.48 cm and is the basic unit in the ft - lb - sec system still often used in the US rather than the m - kg - sec system of SI.

The circumference of the 8 inch wheel is the diameter times pi.

(8 in / 12 (in/ft))π = 2.094 feet

making this wheel turn at 400 revolutions per minute where a point on the outer rim of the wheel travels 2.094 feet for each revolution gives a velocity of

400 rev/min (2.094 ft/rev) = 837.76 ft / min