9 - 0.6x = 1.8
0.6x = 9 - 1.8
0.6x = 7.2
x = 7.2÷0.6
x = 12
80（x + 3）= 400
x + 3 = 400 ÷ 80
x + 3 = 5
x = 5 - 3
x = 2