To solve this problem you must apply the proccedure shown below:
1. You have that the following information given in the problem above: The photograph is reduced by a scale factor of 3/8 and the original had a length of 20 inches,
2- Therefore you have:
length=20 inches-(20 inches x 3/8)
length=20 inches-7.5 inches
length=12.5 inches
3- Then, as you can see, the answer is: 12.5 inches.