The water pressure at the surface of the ocean is  lb/in.

(a)

Consider  is the water pressure and  is the depth of the water level.

Pressure and depth are linearly related : .

Where  is the slope.

At the surface of the ocean, the depth is zero and Pressure is lb/in.

The water pressure is .

The water pressure increases by lb/in for every  ft.

Slope is .

Substitute in .

The water pressure as a function of depth is .

(b)

Water pressure  lb/in.

Substitute  in the Pressure function.

The depth of water is  ft.

(a) The water pressure as a function of depth is .

(b) The depth of water at pressure  lb/in is ft.