from all the 247 students, 7 went on by cars, meaning they didn't fit in the buses, so they students that went in the buses are 247 - 7 = 240.
now, we know there were 6 buses, so dividing 240 evenly by 6, 240/6 = 40.
6. 40 minutes (15/3 = 5 minutes/mile) - 5*8 = 40 min
7. 15,840 ft / 5 = 3.168 ft
To find the answer, divide 7.2 miles by 3 hrs, this would get you to answer B, 2.4 miles per hour