47. A, B, and C start running on a circular track with a circumference of 300 meters at the same time, from the starting point and in the directions as shown in the figure. 15 seconds after the start, B and C meet for the first time, and after another 10 seconds, A and B meet for the first time. Then, after $\qquad$ seconds, A will catch up with C for the first time.
answer: 50