The temperature at the inner radius $($r$1=5$ cm$)$ is $125$C and at the outer radius $($r$2=10$ cm$)$ is $60$C in a spherical shell. Calculate the rate of heat flow through, the shell if k of the shell material is $2$ W$/$mK$.$ What would be the temperature of the shell material at a radius of $7\mathrm{.}5$ cm$?$