The diameter is 14 feet; the circumference is 14pi feet.
An hour is 60 minutes.
A mile is 5280 feet.
Use unit conversions to convert rpm to miles per hour; the cable moves at the speed of a point on the circumference of the pulley.
rev 14pi ft 1 mi 60 min mi
x ----- * -------- * --------- * ------- = 11 ----
min 1 rev 5280 ft 1 hr hr
= 22.009
To the nearest tenth, the rate of rotation of the pulley to get a speed of 11 mph is 22.0 rpm.