To convert miles to feet, you can use the conversion factor that there are 5,280 feet in one mile.
To find the number of feet in 3.5 miles, you can multiply the number of miles by the number of feet per mile:
\[ 3.5 \text{ miles} \times 5,280 \text{ feet/mile} = 18,480 \text{ feet} \]
Thus, there are 18,480 feet in 3.5 miles.