solve every thing step by step$//$ A hot surface is cooled by attaching fins $($called pin fins$)$ to it$,$ as shown in Figure P$13-16.$ The surface of the plate $($left end of the pin$)$ is $90C.$ The fins are $6$ cm long and have a cross$-$sectional area of $5{10}^{-6}{m}^2$ with a perimeter of $0\mathrm{.}006$ m $.$ The fins are made of copper