1. The problem statement, all variables and given/known data find d/dt for a rectangle. 2. Relevant equations A=bh product rule for derivatives (the first times the derivative of the second plus the second times the derivative of the first) Chain rule for derivatives 3. The attempt at a solution If b is a constant, then I know that dA/dh = b (this was the previous problem in which I could solve) my issue with the current problem is that this variable t that I'm supposed to take the derivative with respect to is not in the problem- so how would I go about doing this? My attempt: d/dt (A=bh) dA/dt = bh dA/dt = (b(dA/dh)) + (h(dA/db)) My only problem with this solution is that I think there should be a d(b or h)/dt on the right side of the equation because of the chain rule could someone please explain where/why the variable t comes in and what the correct answer is? Thank you!!