Cold conditioned air at $12C$ is flowing inside a $1\mathrm{.}5$ cm thick square aluminum $\frac{W}{m}.C)$ duct of inner cross section $22cm22cm$ at a mass flow rate of $0\mathrm{.}8k\frac{g}{s}.$ The duct is exposed to air at $33C$ with a combined convection$-$radiation heat transfer coefficient of $8\frac{W}{m^2}.C.$ The convection heat transfer coefficient at the inner surface is $75\frac{W}{m^2}C.$ If the air temperature in the duct should not increase by more than $1C$ determine the maximum lenght of the duct.

Can you help me with a drawing showing resistances and also formulas in detail. Thank you so much