With the bottom of the Ferris Wheel being 5 meters off the ground, and a radius of, r = 7.5 meters, the center of the Ferris Wheel is 12.5 meters off the ground.
A horizontal line through the center of the Ferris Wheel is 12.5 meters off the ground, and therefore the lower half of the Ferris Wheel is always below 14 meters.
The distance from the horizontal to 14 meters is 1.5 meters (14 - 12.5), and angle between the horizontal and a radius to 14 meters is sin(θ) = 1.5/7.5 or θ = sin-1(1.5/7.5) = 11.54o. This angle height is on both sides of the Ferris Wheel and therefore 180o + 2*11.54o = 203.07o is always under 14 meters. What is above 14 meters is 360o - 203.07o = 156.93o.
Since it takes 8 minutes for 1 revolution, (156.93o/360o)*8 min ≈ 3.5 min, the amount of time the Ferris Wheel is above 14 meters.
I do hope this is helpful! :)