This is not correct. You need to know the Ground Speed (or the TAS) to calculate the Rate of descend at a 3.1° angle, with trigonometry. In this case 500ft/min only works if the GS is 93KT to reach 32NM(=60km) ground distance in 21 mins. (calculated 21mins with 500fpm from 10500 ft (=3200m)).
