X$.$ A horizontal large plate with $2m^2$ is maintained at $85C$ and exposed to atmospheric air at

$15C.$ Calculate the free$-$heat transfer if plat is $2$ m high and the air properties are:

$k=0\mathrm{.}03\frac{W}{m}.C$

$v=12\mathrm{.}3{10}^{-6}\frac{m^2}{s}$

$Pr=1\mathrm{.}2$