a)What direction should I start for fastest descent?

b)If I travel in the direction of fastest descent at 2 meters/sec., what will be my rate of descent?

c)derive an expression for this rate of descent as a function of the direction traveled and the speed in that direction.

d)in what directions should I start in order NOT to go up or down?

I know how to find directional derivatives and gradient vectors but I am used to questions in a format where I am given the functions. I know the gradient vector gives the direction of fastest increase of such a function (travelling perpendicularly down level curves). However, I am not very good at applying my knowledge!