3) 7\16+(-11\42)+(-9\16)+17\42 =17/42-11/42-9/16+7/16=
=6/42-2/16=1/7-1/8=(8-7)/56=1/56
4)-9\40+13\50+(-23\50)+19\40=
=-23/50+13/50+19/40-9/40=-10/50+10/40=
=-1/5+1/4=(-4+5)/20=1/20
5)-3 31\36+(-1 17\24)+5 4\36+(-2 4\24)=
=-2 4/24-1 17/24-3 31/36+5 4/36=
=-2 4/24-1 17/24 +4 40/36-3 31/36=
= -3 21/24+1 9/36=-3 7/8+1 1/4=
=(-31+10)/8=-21/8=-2 5/8