A U$-$tube manometer indicates a pressure drop of $10$ in$.$ water across an air filter. The air is at $26\backslash$deg C and a gauge pressure of $60$ lb$,$in$\text{'}.($a$)$ What is the pressure drop in lb$,/$in$*$ and in atm? $($b$)$ What percentage of error is introduced if the density of the air in the manometer leads is neglected?