5/7-（2/3-2/5）+3/2
=5/7-4/15+3/2
=150/210-56/210+315/210
=409/210
15/14-2/5+1/15-3/5+6/5
=15/14-6/15+1/15-9/15+18/15
=15/14+4/15
=225/210+56/210
=281/210