In certain deep parts of oceans, the pressure of sea water, $P,$ in pounds per square foot, at a depth of $d$ feet below the surface, is given by the following equation:

$P=16+\frac{4d}{11}$

If a scientific team uses special equipment to measures the pressure under water and finds it to be $400$ pounds per square foot, at what depth is the team making their measurements?

Answer: The team is measuring at feet below the surface.