In regards to pressure ( ch. static fluids - introductory physics)

i am not sure how to apply the equation below with respect to pressure 2.

p1 = p2 + "row"g "delta-y-"
row= density

my question:
when do i include/exclude the {p2} term?

Explanation:

P₁ = P₂ + ρgh

g is the acceleration due to gravity

ρ is the density of the fluid

h is the depth of the fluid

P₁ is the pressure at that depth

P₂ is the pressure at the surface

P₁ and P₂ can either be absolute pressures or gauge pressures, but they must match.

For example, if you wanted to find the absolute pressure at the bottom of an open tank, you would use P₂ = Patm = 14.7 psi or 101.3 kPa.

If instead you wanted to find the gauge pressure, you would use P₂ − Patm = 0 psi or 0 kPa.

If the tank is sealed and pressurized, you would use the P₂ of the tank.

b.transmitters send radio waves, and receivers capture radio waves.

i am pretty sure it is c because when people are closer together, they cannot move as freely. picture being in a mostly full elevator, for instance. the people are right next to you, and you can barely move.