72×0.81+8.1×2.8=7.2x10x0.81+8.1x2.8=7.2x8.1+8.1x2.8=8.1x(7.2+2.8)=8.1x10=81
72×0.81+8.1×2.8= 7.2×8.1+8.1×2.8= 8.1×10= 81