400
S20=20(2(6.5)+(20-1)(12,7))/2
=2543m
In the skydiving lesson by Mr.Leung, Ankush jumps out of plane and falls 6.5m during the first second. For each second afterward, he continues to fall 12.7m more than the previous second. After 20s, he opens his parachute. How far did Ankush fall before he opened his parachute?