Referring to the contour map in Figure 2: (a) Estimate the average rate of change of elevation

Question:

Referring to the contour map in Figure 2:
(a) Estimate the average rate of change of elevation from A to B and from A to D.
(b) Estimate the directional derivative at A in the direction of v.
(c) What are the signs of ƒ_x and ƒ_yat D?
(d) At which of the labeled points are both f_xand f_y negative?

B A V 750 .C D 650 400