x = 90 * 100
x = 9000
1200 : x = 60
x = 1200 : 60
x = 20
30 ⋅ x = 1800
x = 1800 : 30
x = 60
x : 18 = 30
x = 30 ⋅ 18
x = 540
Ответ: x = 9000; x = 20; x = 60; x = 540