The formula which relates Distance, av.Speed and Time is
[tex]Distance=Speed\cdot Time[/tex]
The maximal Distance would be covered if the average speed was 6.3 miles per hour.
In that case D=6.3 (mi/h) * 2 h = 12.6 mi
thus, if x represents the number of miles, x≤12.6 mi
Answer: x≤12.6 mi