$13175$ Two very large parallel plates are maintained at uni$-$form temperatures T$1=750$K and T$2=500$K and have emis$-$sivities $1=0\mathrm{.}85$ and $2=0\mathrm{.}7,$ respectively. If a thin aluminum sheet with the same emissivity on both sides is to be placed between the plates in order to reduce the net rate of radiatio