An aircraft is maintaining a 5.2% gradient is at 7 NM from the runway, on a flat terrain; its height is approximately:

The aircraft is 7 NM or 42,476 ft (7 × 6068) from the RWY.

The gradient is given as 5.2%; so it's simply a case of multiplying the distance from the RWY by the gradient:

42476 × (5.2/100) = 2208.752 ft

Or do it on the whizz wheel; (much quicker)

Put 10 on the inner scale next to the gradient (5.2%) on the outer scale, go to distance from touchdown (42,500ft) on the inner scale and read height above touchdown on the outer scale: 2,210ft.