physics! please help
posted by Tiffany .
A long distance swimmer is able to swim through still water at 4km/hr. She wishes to swim from Port Angeles, WA due north to Victoria, B.C., a distance of 50km. An ocean current flows through the Strait of Juan de Fuca from west to east at 3km/hr. In what direction should she swim to make the crossing along a straight line between the two cities?

Draw a vector diagram. The velocity with respect to ground has to point directly across from PA to Victoria. It is also the vector sum of the water speed and the swimmer's velocity.
Use trig functions to get the angle you need. 
the thing is. i don't know what to do witht the 50km cuz its different units from the 3km/hr and the 4km/hr

velocity, speed, and inertia!I DON'T GET IT!!