Răspuns :
a = b + 12
a + b = 84
b + 12 + b = 84
2b = 84 - 12
2b = 72
b = 72 : 2
b = 36
a = 36 + 12
a = 48
a + b = 84
b + 12 + b = 84
2b = 84 - 12
2b = 72
b = 72 : 2
b = 36
a = 36 + 12
a = 48