A stationary company makes three type of pens: thick point, fine point and highlighter. The cost function is given by C(a,b,c) = 0.

A stationary company makes three type of pens: thick point, fine point and highlighter. The cost function is given by C(a,b,c) = 0.5a2 +2b2 +60a+75b+3c2 +100, where a, b and c stand for the pens manufactured, in the order as mentioned above.

A) Compute the marginal cost with respect to the three variables, when a = 10, b = 15 and c = 30, and explain the result from an economic viewpoint.