A ball is thrown straight up at an initial velocity of 53 feet per second. In the first 1.5 seconds, it travels 42 feet. The formula X = (u+ t over n) t; represents the vertical distance x that an object travels in 7 seconds, where u represents the initial velocity of the object and n represents the velocity of the object at the end of t seconds. Find the velocity of the ball at the end of 1.5 seconds.