A car is driving northwest at $v$ mph across a sloping plain whose height, in feet above sea level, at a point $N$ miles north and $E$ miles east of a city is given by $$h(N,E) = 1750 + 125 N + 25 E.$$ (a) At what rate is the height above sea level changing with respect to distance in the direction the car is driving?
rate =

(b) Express the rate of change of the height of the car with respect to time in terms of $v$.
rate =