Could you please explain how the Optimum Point will be C? It can be B too. When moving the Iso Contribution Line to the further vertex it is coming to B and C.
The contribution line would only come to both B and C if is was parallel to the labour line.
It is not parallel to the labour line (it is a little steeper) and if you move it away from the origin whilst keeping it parallel, then the furthest point away in C and not B.
Have you watched my free lectures on linear programming?