The captain of a boat wants to travel directly across a river that flows due east. He starts from the south bank of the river and heads toward the north bank. The boat has a speed of $5.57 \mathrm{~m} / \mathrm{s}$ with respect to the water. The captain steers the boat in the direction $315^{\circ} .$ How fast is the water flowing? Note that $90^{\circ}$ is east, $180^{\circ}$ is south, $270^{\circ}$ is west, and $360^{\circ}$ is north.