Apostage stamp 25 millimeters wide and 40 millimeters tall is enlarged to make a poster. the poster is 4 feet wide. find the height of the poster.

I come from a place that does not use feet as a measurement metric, so I googled the conversion metrics (correct me if I am wrong)
 


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Find the scale factor between the stamp and the poster
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Stamp : Poster
25mm : 4 feet
25mm : 4 x 304.8
25mm : 1219.2mm
1mm : 48.768mm



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Find the missing height
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Stamp : Poster
40mm : 40 x 48.768mm
40mm : 1950.72mm



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Convert back to feet
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40mm : 1950.72 ÷ 304.8 ft
40mm : 6.4 ft


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Answer
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Height of the poster is 6.4ft