176- In the figure below, mercury is placed on both sides of a U-shaped tube with cross-sectional area $1\ \text{cm}^2$. From one side of the tube, the volume of mercury is $21\ \text{cm}^3$. We pour mercury and raise the air column on the closed side to $15\ \text{cm}$. What is the atmospheric pressure in centimeters of mercury? (The temperature inside the closed tube is assumed to be constant.) [Figure: A U-tube with mercury, closed on one side, with height $18\ \text{cm}$ marked] (1) $73$ (2) $74$ (3) $75$ (4) $76$
\textbf{176-} In the figure below, mercury is placed on both sides of a U-shaped tube with cross-sectional area $1\ \text{cm}^2$. From one side of the tube, the volume of mercury is $21\ \text{cm}^3$. We pour mercury and raise the air column on the closed side to $15\ \text{cm}$. What is the atmospheric pressure in centimeters of mercury?
(The temperature inside the closed tube is assumed to be constant.)
\textit{[Figure: A U-tube with mercury, closed on one side, with height $18\ \text{cm}$ marked]}
\hfill (1) $73$ \hfill (2) $74$ \hfill (3) $75$ \hfill (4) $76$