1. (2023一下·乐山) 细心算，我能算对 

12-4=	87-4=	14-5=	17+9=	14-7=
81-5=	30+24=	81+6=	51-20=	52+9=
61-2=	30+56=	20+45=	55-7=	75-5=
30+(15+5)=	26-(15-9)=	30+(34+5)=	70-(18-9)=	46-(20+20)=
24+2-1=	35+5+20=	63-9-30=