3.52×0.79-0.173×7.9+1.79×0.21
=3.52×0.79-1.73×0.79+1.79×0.21
=(3.52-1.73)×0.79+1.79×0.21
=1.79×0.79+1.79×0.21
=1.79×(0.79+0.21)
=1.79×1
=1.79