If the inner and outer walls of a container are at different temperatures, the rate of change of temperature with respect to the distance from one wall is a function of the distance from the wall. Symbolically, this is stated as $d T / d x=f(x),$ where $T$ is the temperature. If
$x$ is measured from the outer wall, at $20^{\circ} \mathrm{C},$ and $f(x)=72 x^{2},$ find the temperature at the inner wall if the container walls are $0.5 \mathrm{cm}$ thick.