7. The total weekly revenue (in dollars) of the Country Workshop realized in manufacturing and selling its rolltop desks is given by
R(x, y) = -0.2x2 - 0.25y2 - 0.2xy + 200x + 160y
where x denotes the number of finished units and $y$ denotes the number of unfinished units manufactured and sold each week. The total weekly cost attributable to the manufacture of these desks is given by
C(x, y) = 100x + 70y + 4000
dollars. Determine how many finished units and how many unfinished units the company should manufacture each week in order to maximize its profit. What is the maximum profit realizable? (10 分)