$12\mathrm{.}18($a$)$ Calculate the overall heat transfer coefficient for a single$-$pane glass window exposed to $70\backslash$deg F indoor air and $0\backslash$deg F outdoor still air. The thickness of the single$-$pane glass is inch, and the height is $4$ feet. $($b$)$ Calculate for double$-$pane glass with a inch air layer between the panes. The thermal conductivity of the glass is $0\mathrm{.}4$ Btu$/$h$$ft$\backslash$deg F$.$