7.2乘以99+7.2=7.2×(99+1)=7.2×100=720
7.2*99+7.2=7.2*(99+1)=7.2*100=720
7.2*(99+1)=7.2*100=720
=7.2×(99+1)=7.2×100=720
7.2*99+1