36 - 9 × a = 9
9 × a = 36 - 9
9 × a = 27
a = 27 : 9
a = 3
16 + b × 4 = 32
b × 4 = 32 - 16
b × 4 = 16
b = 16 : 4
b = 4
81 - c : 9 = 27
c : 9 = 81 - 27
c : 9 = 54
c = 54 × 9
c = 486
d : 5 + 15 = 25
d : 5 = 25 - 15
d : 5 = 10
d = 10 × 5
d = 50
Verific: 50 : 5 + 15 = 10 + 15 = 25
n × 5 - 5 = 40
n × 5 = 40 + 5
n × 5 = 45
n = 45 : 5
n = 9
V: 9 × 5 - 5 = 45 - 5 = 40