0.75*3.6*10.7=3/4*3.6*10.7=2.7*10.7=2.7*10+2.7*0.7=27+1.89=28.89
原式=7.2x3.6+7.2x6.4=7.2x(3.6+6.4)=7.2x10=72
0.75x102=0.75（100+2）=0.75x100+0.75x2=75+1.5=76.5
