Calculate the pressure of the gas samples as indicated by the manometer

**Part A)** Given a barometric pressure of $\pu{764.0 mmHg}$, calculate the pressure of gas sample (a) as indicated by the manometer.  

![enter image description here](https://i.stack.imgur.com/P2lqb.jpg)


**Part B)**
Given a barometric pressure of $\pu{764.0 mmHg}$, calculate the pressure of gas sample (b) as indicated by the manometer.  

![enter image description here](https://i.stack.imgur.com/Ijv7m.jpg)


For Part A) I tried to subtract $764.0-40.0$ to get $724$ but the answer is wrong.  

For Part B) I tried to add $764.0+40.0$ to get $804$, but the answer is also wrong.




In part (A), ${\rm P}\_{\rm gas} > {\rm P}\_{\rm atm}$, as evidenced by the column of mercury being "pushed up" in the manometer on the side of ${\rm P}\_{\rm atm}$ - in this case, you'll need to add (the amount it's "pushed up") to atmospheric pressure (i.e., 764 mm Hg). You state that you tried to subtract 40.0 from 764.0: Look at the graphic again (I hold it's 7 cm - or 70 mm - Hg) and try adding that number to 764 mm Hg instead of 40 mm Hg.


For part (B), ${\rm P}\_{\rm atm} > {\rm P}\_{\rm gas}$, so reverse the process above. I believe what you state is your answer to part (A) is actually the correct answer to part (B).


 2