this is just a basic proportion problem. we are comparing the RATIO of the height to length. so the ratio would b 
height height
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length length . the numbers it gives us are 2 to 25 so substitute those in on the same side since they go together. 
24 2
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x 25. they also told is that the height of the window is 24 so put that on the top too because its length. then just cross multiply to get 2x=600 
then divide and get the answer of x=300