Yes, your result is correct. You haven't explained how you got from the 3rd line to the 4th line though.
It's also simple to prove by setting Y = AB, therefore X = ABC + (AB)'C becomes X = YC + Y'C = C(Y + Y'), from which it's obvious that Y is irrelevant (Y+Y' = 1) and that X = C.
The other common way of showing e.g. "A-bar" is /A