①5x+7=28
②6.6x+5.4x=19.2
③4x-0.7 =8.1
④12+5x=72
⑤7.5+2.5x=15
⑥x-0.85x=3
①x-39.87=25.59
②6x+56= 80
③x÷5=42.8+74.5