Hello!
We can write this as a proportion below.
[tex] \frac{blueprint}{real} = \frac{0.5}{4} = \frac{18}{x} [/tex]
As you can see, 4 is eight times 0.5. Therefore, we can multiply eighteen by eight to get our answer.
18(8)=144
Just to check, we can cross multiply and divide.
72/0.5=144
Therefore, our answer is 144 feet.
I hope this helps!