4. (10 points) The ticket price for a friendly football match is 50 yuan. An hour before the game, there were still tickets left, so the price was reduced. As a result, the number of tickets sold increased by one-third, and the box office revenue increased by one-quarter. Therefore, the price of each ticket was reduced by ( ) yuan.
A. 10
B. $\frac{25}{2}$
C. $\frac{50}{3}$
D. 25