A spherical Pyrex glass shell has inside and outside diameters of D₁ = 0.1 m and D₂ = 0.2 m, respectively. The inner surface is at T_s,1 = 100°C while the outer surface is at T_s,2  = 45°C.

(a) Determine the temperature at the midpoint of the shell thickness, T(r_m = 0.075 m).

(b) For the same surface temperatures and dimensions as in part (a), show how the midpoint temperature would change if the shell material were aluminum.