7-[100x52:13-5x(3x120-2xa)]:20=2
7-[5.200:13-5x(360-2xa)]:20=2
7-[400-5x(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
