870..... плиз 20 баллов

(7/15+7/30+4/5):(2-1/3-1/2)=((14+7+24)/30):((12-2-3)/6)=45/30:7/6=9/6*6/7=9/7=2целых 2/7 (1/6+1/10+1/15):(3/5-1/3-1/4)=((5+3+2)/30:(36-20-15)/60=10/30:1/60=1/3*60/1=60/3=20