Find the limiting velocity

This is a question i got, which i have NO CLUE how to solve, or what they are asking. Can I please get some help??

It reads:

The velocity of a body of mass m falling from rest under the action of gravity is given by the equation $\displaystyle \mbox{v}= \sqrt {\frac{mg}{k}}\mbox{tanh}\ ( \sqrt{\frac{gk}{m} \mbox{t}}) $, where k is a constant that depends on the body's aerodynamic properties and the density of the air, g is the gravitational constant, and t is the number of seconds into the fall. Find the limiting velocity, $\displaystyle \lim_{\mbox{t}\rightarrow\infty} \mbox{v} $, of a 340lb skydiver (mg = 340) when k=0.006.