Question

4. A swimming pool of width 9.0 m and length 24.0 m is filled with water to a depth of 3.0 m.

Calculate pressure on the bottom of the pool due to the water.

Answer 1

pressure on bottom is due to 2 things : due to water in the pool and due to atmospheric pressure . 
since you are asking pressure due to water , is density 
x g x height 
=  1000 x 10 x 3           because water density = 1000 kg/m^3
= 30000 N 
 if u want total pressure u can add atmospheric pressure to this . 
hope you understood .

Answer 2

Pressure = height from surface x density of water x g (acceleration due to gravity)
= 3 x 1000 x 9.8 Pascal
= 29400 Pascal