Pa = atmospheric pressure (look it up in units of N/m^2)
D = density of water (given as 1000 kg/m^3)
h = depth of water = 3m
g = acceleration of gravity = 9.8 m/s^2
At a depth of h (meters), the static pressure is
P(h) = Pa + Dgh
Plug in the numbers and get P(h) in units of N/m^2.