Easy Math/Science question?

You would have to know the cross section and other things about the man, so that you could determine what his terminal velocity(the fastest speed he could be going) is. When jumping from that distance, he would reach terminal velocity. Once you figured out that speed, you would have to figure out what the buoyant force of the water is and in order to determine this you would have to know what the volume of the man is. Using the force from the water and the force of gravity you could find his acceleration in the water. Using this acceleration and his initial speed you can figure out the distance. So it is impossible to answer without more information.