A DME station is located 1000 feet above MSL. An aircraft flying at FL 370 in ISA conditions which is 15 NM away from the DME station, will have a DME reading of:

These are best answered using Pythagoras' Theorem.

DME Range^2 = Ground Range^2 + Height^2

Ground Range = 15 NM

Height = 37000 - 1000 (ABOVE MSL) = 36,000 (Divided by 6,080 = ~6 NM) - Accurate enough!

DME^2 = (15 x 15) + (6 x 6)

DME^2 = 225 + 36

DME^2 = 261

DME = SQRT (261)

DME = 16.15 NM