72 - x = 18 * 3
72 - x = 54
x = 72 - 54
x = 18

x : 8 = 130 + 270
x : 8 = 400
x = 8 * 400
x = 3200

400 : x = 1.000 : 10
400 / x = 1000 / 10
40/x = 100
40 = 100x
x = 40 / 100
x = 0.4