(-11/15)*(-10/11)*(-9/10)+(-7/9)*(-6/7)+4/15=
-(11/15)*(-10/11)*(-9/10)+(-7/9)*(-6/7)+4/15= -3/5+2/3+4/15= 5/15= 1/3
-990/1650=-99/165=-33/55=-3/5 -7/9*(-6/7)=2/3 4/15+2/3-3/5=4/15+10/15-9/15=5/15=1/3