38 + x = 72
x = 72 - 38
x = 34
x - 31 = 45
x = 45 + 31
x = 76
x : 4 = 20
x = 20 · 4
x = 80
6 · y = 18
y = 18 : 6
y = 3
b : 7 = 5
b = 5 · 7
b = 35
36 : c = 9
36 : 9 = c
c = 4
