a, `12 + 126 + 42 + 74 + 158 + 88`
`= (12+88)+(126+74)+(42+158)`
`=100+200+200`
`=500`
b, `15xx23+15xx56+15xx21`
`=15xx(23+56+21)`
`=15xx100`
`=1500`
a
12+126+42+74+158+8812+126+42+74+158+88
=(12+88)+(126+74)+(42+158)=(12+88)+(126+74)+(42+158)
=100+200+200=100+200+200
=500=500
b
15×23+15×56+15×2115×23+15×56+15×21
=15×(23+56+21)=15×(23+56+21)
=15×100=15×100
=1500
a, 12+126+42+74+158+8812+126+42+74+158+88
=(12+88)+(126+74)+(42+158)
=(12+88)+(126+74)+(42+158)
=100+200+200=100+200+200
=500=500
b, 15×23+15×56+15×2115×23+15×56+15×21
=15×(23+56+21)
=15×(23+56+21)
=15×100=15×100
=1500
