可变化为280×36+720×36=（280+720）×36=36000
280*36+360*72=360*28+360*72=（28+72）*360=36000
280×36+360×72=28×10×36+360×72=（28+72）×360=
原式=28x360+360x72 =360x(28+72) =360x100 =36000
