Okay so changing from 6 inches to 5 feet is a 1:10 ratio (since 5 (feet) x 12 (inches) = 60 (inches) this gives you a 6 (original inches): 60 (inches after enlarging) ratio, which is simplified to 1:10 when you simplify both sides by a factor of 6.
So, let’s plug the 3 feet into this ratio. 3 feet is equal to 36 inches. This gives you 3.6 inches. (Since 3.6 times 10 is 36)
Hope this helps!!