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