Use the ideal gas equation PV=nRT. You can compare before and after using P1V1/n1T1=P2V2/n2T2. Since the number of moles remains constant you can disregard moles from the equation and use pressure, volume and temp. Make sure your pressure is converted to atmospheres, your volume is in liters, and your temperature is in kelvins.
As per Le Chatelier principle, when a system in equilibrium is disturbed, the reaction will try to compensate the change to restore the equilibrium.
This reaction occurs in gas phase, so the volume is inversely proportional to the pressure.
Then a decrease in volume will cause an increase in pressure, so the system will tend to react in the direction that compensates this increase, this is the system will try to reduce the number of moles of particles to reduce the increase of the pressure.
As you see, there are 3 particles of products (2 of NO and 1 of Br) for every 2 particles of reactant (NOBr).
That means, that the equilibrium will displace to the left, this is the concentration of NOBr will increase while the concentration of NO and Br will decrease.
Since phosphoric acid is H3PO4, which is known from PO4, with a charge of 3- so 3 hydrogen would balance it out, and sodium hydroxide is NaOH, it can be assumed that it results in H3(OH)3 + Na3PO4.
