To solve the problem $,$ subtract the average thickness $($d$)$ of the cooler from each of the cooler's dimensions, then use these reduced dimensions to calculate the surface area. With this surface area, you can then use the Q$/$t $=$ k$*$A$*($T$\_2-$ T$\_1)/$d

question$-$ A styrofoam cooler $($K $=\mathrm{.}030$ W$/$mo C$)$ has outside dimensions of $0\mathrm{.}130$ m x $0\mathrm{.}350$ m x $0\mathrm{.}380$ m$,$ and an average thickness of $2\mathrm{.}6$ cm$.$ About how long will it take for $1\mathrm{.}60$ kg of ice at $0$o to melt in the cooler if the outside temperature is $30\mathrm{.}0$o$?$