5. A baseball diamond is a square with side 90 feet. A batter hits the ball and runs toward first base with a constant speed of 25 feet per second. At what rate is his straight-line distance from second base changing when he is two thirds of the way to first base? (Hint: \"straight-line distance\" means the distance of the line segment from the batter to second base, not the remaining distance the batter has to run along the baselines)