What is the external$-$internal pressure difference when the diver's lungs are at a depth of hh $=5\mathrm{.}6$ mm $($about $18$ ftft $)?$ Assume that the diver is in fresh water. $($A scuba diver breathing from compressed air tanks can operate at greater depths than can a snorkeler, since the pressure of the air inside the scuba diver's lungs increases to match the external pressure of the water.$)$