x • 8 = 56
x = 56 :8
x = 7
7 • 8 = 56
56 = 56

x : 4 = 17
x = 17 • 4
x = 68
68 : 4 = 17
17 = 17

90 : x = 5
x = 90 : 5
x = 18
90 : 18 = 5
5 = 5