a + b = 12
b + c = 12
atunci si
a + c = 12
2a + 2 b + 2 c = 36
2 ( a + b + c ) = 36
a + b + c = 36 : 2
a + b + c = 18
12 + c = 18
c = 18 - 12
c = 6
b + c = 12
b + 6 = 12
b = 12 - 6
b = 6
a + b = 12
a = 6 + 12
a = 12 - 6
a = 6
6 a + 9 b +3c = 6 x6 + 9 x6 + 3 x6 = 36 + 54 + 18 = 108
