Here's my question:
A metal bar is heated to a certain temperature and then the heat source is removed. At time t minutes after the heat source is removed, the temperature, x degrees Celcius, of the metal bar is given by $x = \dfrac{280}{1+0.02t}$ At what rate is the temperature decreasing 100 minutes after the removal of the heat source?
I'm guessing the chain rule needs to be employed; as in $\dfrac{dx}{dt} = \dfrac{dx}{du}\dfrac{du}{dt}$ but couldn't figure out exactly how? Help appreciated, thanks!