33 + c = 66 => c = 33
b = 55 - 33 = 22
a = 33 - 22 = 11
a+b+c=66
a+b=33 -> a= 33-b
b+c =55 -> c= 55-b
33-b + b + 55-b= 66 (se simplifica -b cu +b)
33+55-b=66
88-b =66
-b = 66-88
-b = -22 (inmultim cu -1)
b=22
