The figure below shows an object whose mass is $6\mathrm{.}68$ lbm attached to a rope wound around a pulley. The radius of the pulley is R $=3\mathrm{.}97$ in$.$ If the mass is lowered at a constant velocity of $3\mathrm{.}75$ ft$/$s$,$ determine the rotational speed of the pulley, in revolutions per minute $($rpm$).$ The acceleration of gravity is g $=32\mathrm{.}2$ ft$/$s$2.$