$5$: You want to cross a $324m$ wide river and arrive at a dock that sits $172m$ upstream from where you start. You take a boat with a speed $($measured in still water$)$ of $1\mathrm{.}9\frac{m}{s}$ and find that you must angle your boat at exactly $45$ to shore to reach the dock on a straight line path. What is the velocity of the river's current. Please draw a picture to accompany this problem.