-9/7×(-28/3)÷6/15
=-9/7×(-28/3)÷2/5
=-9/7×(-28/3)×5/2
=-(9×28×5)/(7×3×2)
=-1260/42
=-(1260÷42)/(42÷42)
=-30
-3/25+(-24/15)÷21/35
=-3/25-8/5÷3/5
=-3/25-8/5×5/3
=-3/25-40/15
=-3/25-8/3
=(-9-200)/75
=-209/75
-2/3×6/8-3/4÷1/-2
=-2/3×3/4-3/4×(-2)
=-6/12+6/4
=-6/12+3/2
=(-6+18)/12
=12/12
=(12÷12)/(12÷12)
=1