I would like the process to get the answer that is given:

A thin stainless$-$steel disk of thickness b and the outer radius $r_0$ has been heated treated to a high, uniform initial temperature of $T_i.$ The disk is then placed upon a small stand and allowed to cool. The ambient air and surrounding are at $T_{}$ and $T_{\text{s}\text{u}\text{r}\text{f}},$ respectively. The convection coefficients on the top and bottom disk surfaces, $h_t$ and $h_b,$ are known. As is the plate emissivity, $lon.$ Derive a differential equation that could be solved to determine the transient thermal response of the disk, $T(r,t).$ List the appropriate initial and boundary conditions.

FIND: Derive differential equation governing transient temperature distribution, $T(r,t).$ List initial and boundary conditions.

Initial

ANSWER IS GIVEN BELOW!

$)]=[(r^4)=(0|=0,\frac{\text{d}\text{e}\text{l}\text{T}}{\text{d}\text{e}\text{l}\text{r}}{|}_r|=r=0$