Final answer:
The velocity at the highest point of a ball's trajectory is its initial horizontal velocity, which is 16 m/s in this case.
Step-by-step explanation:
The velocity of a ball at the highest point of its trajectory is due solely to its horizontal component, as the vertical component of velocity becomes zero at the peak. In the scenario provided where the ball is kicked with an initial horizontal velocity of 16 m/s and a vertical velocity of 12 m/s, the velocity at the highest point will be the initial horizontal velocity, as there is no vertical velocity at the highest point. Therefore, the velocity at the highest point of the ball's trajectory is 16 m/s, which means that none of the given options (a) 15 m/s, (b) 10 m/s, (c) 12.99 m/s, and (d) 7.5 m/s are correct if they are intended to represent the horizontal velocity.