Alexa started a race with a 50 meter head start. she ran at a pace of 6.25 meters per second. after how many seconds was alexa 200 meters past the starting line?

-- She was 50 meters from the starting line when the gun sounded.

-- In order to get 200 meters from it, she has to run another (200-50)= 150 meters.

-- Running 150 meters takes her  (150/6.25) = 24 seconds.