In Exercises 5-13, sketch a contour diagram for the func- tion with at least four labeled contours. Describe in words the contours and how they are spaced. 5. f (x, y) = x+y 6. f(x, y) = 3x + 3y 7. f(x, y) = x2+ 1 8. f (x, y) =-x- >+1 9. f (x, y) = xy 10. f(x, y ) = y - x2 11. f(x, y) = x2+ 232 12. f(x, y) = Vx2+2,2 13. f(x, y) = cos21. Each contour diagram (a)-(c) in Figure 12.58 shows satisfaction with quantities of two items X and Y com- bined. Match (a)-(c) with the items in (D)-(III). (a) Y (b) Y X () Y 10 X Figure 12.58 (I) X: Income; Y: Leisure time (II) X: Income; Y: Hours worked (III) X: Hours worked; Y : Time spent commuting