1. The problem statement, all variables and given/known data How fast is the volume of a rectangular box changing when the length = 6 cm, width = 5 cm and depth = 4 cm and the length and height are increasing at a rate of 1 cm/s and width is decreasing at a rate of 2 cm/s. 2. Relevant equations Volume of a rectangle = l*w*h 3. The attempt at a solution I know how to solve these kinds of the problems, done about 20 so far. The only trouble I am having is that I don't know which variable to take the derivative with since I have 3. I just can't figure out where to start this problem.