Sounds like 10.0 ft refers to the height/diameter of the wheel, in which case its radius is 5.0 ft.
In one complete revolution, a point on the edge of the wheel travels 2π*(5.0 ft) = 10π ft, so the point's linear speed (and thus the current's speed) is
(5.0 rev/min) * (10π ft/rev) = 50π ft/min
Convert this to mi/h using
1 mi = 5280 ft
1 h = 60 min
==> (50π ft/min) * (1/5280 mi/ft) * (60 min/hr) = 1.8 mi/h
