Answer:
4.5 miles
Explanation
Figure out how far the hot air balloon travelled in 1 hour - 3 hours can be divided by 3 for 1 hour, so do the same for the miles - 18 / 3 = 6
So basically, the hot air balloon travelled 6 miles in 1 hour.
Now, you can work out 3/4 of 6 for 3/4 of 1 hour - 3/4 * 6 = 4.5 miles
:)