a) 231+0=231
452+(18+0)=470
452+18=470
(34+0)+(16+0)=50
34+16=50
b) (48+3)+7=58
51+7=58
25+(105+46)=176
25+151=176
134+(149+66)=349
134+215=349
c) (403+57)+(88+122)=668
460+208=668
(40+65)+(95+60)=260
105+155=260
(1091+133)+(1019+150)=2393
1224+1169=2393
d) 14+17+6+3=40
31+6+3=40
37+3=40
180+15+45+20=260
195+45+20=260
240+20=260
38+62+53+21+47=221
100+53+21+47=221
153+21+47=221
174+47=221
