The Castle of Beynac is 400 meters from the Dordogne river as measured from the closest point P in center of the river. If Veronica is floating down the center of the river in a canoe at a rate of 6 meters/second, how fast is her distance to the castle changing when she is 250 meters upstream from point P. You can assume that the river is straight on this stretch and ignore any issues of elevation. Answer (in meters per second):
