A ball is thrown over the head of a person who is standing a horizontal distance d from the point where the ball was thrown. The initial ball's velocity is at an angle 0 with respect to the ground and has a magnitude vo. As soon as the ball is thrown, the person runs with a time-varying acceleration whose component along the r-axis is given by Bt, where B is a positive constant. The person catches the ball at exactly the same height it was thrown from. Assume that the air resistance is negligible and that the gravitational acceleration is directed downward and has magnitude g. Find the constant B. Express your answer in terms of some or all of the given variables. Use 0, g, d, and vo as needed.