Question

If the atmospheric pressure is 0.975 atm what is the pressure of the enclosed gas

Answer 1

Missing in your question:
Picture (1)
when its an open- tube manometer and the h = 52 cm. 
when the pressure of the atmosphere is equal the pressure of the gas plus the pressure from the mercury column 52 Cm so, we can get the pressure of the gas from this formula:
P(atm) = P(gas) + height (Hg)
∴P(gas) = P(atm) - height (Hg)
              = 0.975 - (520/760) 
              = 0.29 atm
Note: I have divided 520 mm Hg by 760 to convert it to atm
Picture (2)
The pressure of the gas is the pressure experts by the column of mercury and when we have the Height (Hg)= 67mm 
So the pressure of the gas =P(atm) + Height (Hg)
                                             =  0.975 + (67/ 760) = 1.06 atm
Picture (3) 
As the tube is closed SO here the pressure of the gas is equal the height of the mercury column, and when we have the height (Hg) = 103 mm. so, we can get the P(gas) from this formula:
P(gas) = Height(Hg)
           = (103/760) = 0.136 atm