FL360 to FL120 = 24,000'
Rate of Descent = 2,000' fpm
Time to descend = 24,000' / 2,000' = 12
minutes (0.2 hours)
Ground Speed = 420 kts
Distance from Top of Descent to Bottom
of Descent = 420 x 0.2 = 84 NM
Distance from Bottom of Descent to WP =
40 NM
Distance from Top of Descent to
Waypoint = 84 NM + 40 NM = 124 NM