Yes, that is the reason.
So why is "dh/dt" inserted so far down in the steps? is there a better method where it has "dh/dt" from the beginning since thats what we are looking for...
in the end the answer is dh/dt \approx 0.108
Thanks heaps!!!It is there "from the beginning". Your first equation is and then the very next equation is . So you already have the derivative with respect to t in there. Now use the relationship between h and r to write as a function of h only:
(You have an error- the "1/3" accidently became "3")
Now use the chain rule to differentiate with respect to t.