3/2-5/6+7/12-9/20+11/30-13/42
=3/2+7/12-9/20+11/30-13/42-5/6
=18/12+7/12-27/60+22/60-13/42-35/42
=25/12-5/60-48/42
=25/12-1/12-8/7
=2-8/7
=6/7