Mathematics

Lisa gives her little brother Sam a 15-second(sec) head start in a 300-meter(m) race. During the race, Sam runs at an average speed of 5 m/sec and Lisa runs at an average speed of 8 m/sec, not including the head start. Which of the following best approximates the number of seconds that had passed when Lisa caught up to Sam?

A.5
B.25
C.40
D.55

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