0.28×6.1+61×0.072＝0.028×61+61×0.072＝(0.028+0.072)×61＝0.1×61＝6.1
0.28×6.1+61×0.072=0.28×6.1+6.1×0.72=(0.28+0.72)×6.1=1.00×6.1=6.10
