For part a), sketch a right triangle height = 12 ft, hypotenuse = 13 ft. boat speed is horizontal. The speed component along the rope is 4 ft/s. What is the horizontal speed component of the boat? You do not know the angle between the rope and the horizontal, but you can work around it. The second part of the question, is qualitative analysis, what happens to the angle between the horizontal and the rope. Make the connection with the velocity change, does it increase or decrease, justify your conclusion.
Complete part a). If you still need help in part b) repost the question.