(6+9+27+54+99)/3
=6/3+9/3+27/3+54/3+99/3
=2+3+9+18+33
=2+18+3+9+33
=20+12+33
=65300*9.9-200*9.9300*9.9-200*9.9=（300-200）*9.9=100*9.9=990