A pharmaceutical corporation has two plants that produce the same over-the-counter medicine. If x1 and x2 are the numbers of units produced at plant 1 and plant 2, respectively, then the total revenue for the product is given by
R = 200x1 + 200x2 - 4x1^2 - 8x1x2 - 4x2^2
If x1 = 4 and x2 = 12, find the following.
a) the marginal revenue for plant 1, ∂R/∂x1
b) the marginal revenue for plant 2, ∂R/∂x2