The joint cost (in dollars) for two products is given by
C(x, y) = 30 + x2 + 3y + 2xy
where x represents the quantity of product X produced and y represents the quantity of product Y produced.
(a) Find and interpret the marginal cost with respect to x if 8 units of product X and 10 units of product Y are produced.
(b) Find and interpret the marginal cost with respect to y if 8 units of product X and 10 units of product Y are produced.