At the surface of the ocean, the water pressure is the same as the air pressure above the water, 15 $\mathrm{lb} / \mathrm{in}^{2} .$ Below the surface, the water pressure increases by 4.34 $\mathrm{lb} / \mathrm{in}^{2}$ for every 10 $\mathrm{ft}$ of descent.
(a) Express the water pressure as a function of the depth below the ocean surface.
(b) At what depth is the pressure 100 $\mathrm{lb} / \mathrm{in}^{2} ?$