Barometric pressure is the atmospheric pressure; the pressure inside the atmosphere of the Earth.
This reduces the higher the altitude is so is, therefore, a variable to the absolute pressure that must be considered when planning a dive.
This one is pretty straightforward if you know you to navigate the PADI Instructor Manual. As soon as you're asked to define something such as Deep Dives, Altitude or Mastery you should head to the Training Standards section.
This section is super easy to navigate too as it's in alphabetical order.
Whenever administrative questions head straight to the Paperwork and Administrative Procedures section of the Instructor Manual.
The whole section is in alphabetical order and covers everything generally related to the PADI system.
Some more specific items may be found in the first section of a corresponding course but this should be your first port of call.
The constants on PADI exams is always listed at the top of question sheet so there's no need to attempt to memorize them.
This question is in fresh water so the pressure per metre is 0.097 ATM. It's also stating it's looking for the gauge pressure. This means it is zeroed at the surface and doesn't include the pressure exerted by the ambient air.
The sum becomes pretty straightforward once you have this information dialed in. it's depth (16) multiplied by pressure (0.097).