Determine the first partial derivatives (af lax and af /ay) of each. 8. f(x,y)=2x-2y + 2x-3y+4-x.y+x.y 10 f(x,y)=er+3y-2x+3y 9 f(x,y)=e* -In (y) 11. The monthly profit (in dollars) of Bond and Barker Department Store depends on the level of inventory x (in thousands of dollars) and the floor space y (in thousands of square feet) available for display of the merchandise, as given by the equation P(x,y)=-0.02x-15y + xy +39x+25y-20,000 Computer Op/ax and OP/oy when x = 4000 and y = 150. Interpret the results. Repeat with x = 5000 and y = 150 12. The productivity of a country is given by f(x,y)=15.14x0.438 0.562, where x is the amount of labor and y is the amount of capital. Does this represent a Cobb-Douglas Function? Why or why not? b. Determine the partial derivatives f, and f,, then evaluate when x = 69 and y = 53. c. Interpret the results. Is it better to increase labor or capital by one unit? a.