计算下面各题，能简算的要简算

①12.5×4.8

②28.5÷15×5.6

③21÷0.25÷0.4

④0.55×5.6+0.45×5.6

⑤24.6×18-24.6×8.

⑥20.9+8.5÷(5.2-3.5)