①80-(8.8+1.2)×1.4
②86.4÷0.24×0.25
③(455-12.5×4)÷0.81
④12.3-12.3×0.9
⑤12.6÷[3.5-(9.8-8.7)]
⑥1.08÷[(0.4+0.5)×0.6]