a,(-35)+23-(-35)-47
= (-35 +35) + (23 -47)
= 0 -24
= -24
b,24-(-136)-(-70)+15+(-115)
= 24 +136 +70 +15 -115
= (24 +136) + (15 -115) +70
= 160 -100 +70
= 60 +70
= 130
c,37-(-43)+(-85)-(-30)+15
= 37 +43 -85 +30 +15
= (37 +43) + (-85 +15) +30
= 80 -70 +30
= 10 +30
= 40