If you would like to find the minimum number of gallons Haley will need, you can calculate this using the following steps:
18 miles ... 1 gallon
200 miles ... x gallons = ?
18 * x = 1 * 200
18 * x = 200
x = 200 / 18
x = 11.11 gallons
The minimum number of gallons Haley will need is 12 gallons.