Explanation:
The wheel has a diameter of 250 feet, so its circumference is:
C = 2πr = πD
C = 250π feet
It makes one revolution in 30 seconds, or half a minute, so the linear speed of the passenger is:
v = d / t
v = 250π / 0.5
v = 500π ft/min
v ≈ 1571 ft/min
This is about the same as 17.9 mph.