7-[100×68÷17-5×(60×6-2×a)]÷20=2
7-[6800:17-5x(360-2xa)]:20 = 2
[400-5x(360-2xa)]:20 = 7-2
[400-5x(360-2xa)]:20 = 5
400-5x(360-2xa) = 5x20
400-5x(360-2xa) = 100
5x(360-2xa) = 400-100
5x(360-2xa) = 300
360-2xa = 300:5
360-2xa = 60
2xa = 360-60
2xa = 300
a = 300:2
a = 150
