Scale question

[Civil War]

 I understand that O scale is 1-48. How do I figure out the scale length of something like a canal boat that in real life is 72 feet long? What do I multiply the 72 feet by to come up with the scale length? I know it is a stupid question, but I've always had a hard time with math. That is why I am a historian. The only thing I need to know the length of is time.

 Thanks

[joetrains]

 1/48:  1 inch =48 inches  or 4 feet. divide 72 feet by 4 =18 inches = 72 scale feet

multiplying 72 by  point 25 will give the same result.