The equation for speed is
[tex]v\text{ = }\frac{x}{t}[/tex]where x is the distance, and t is the time. In the international system, we have that x must be in mt, and t must be in seconds. But in this case, we don't use the international system. So:
[tex]v\text{ = }\frac{99\text{ miles}}{\frac{11\text{ hours}}{2\text{ }}}\text{ = }\frac{99\text{ miles x 2}}{11\text{ hours}}\text{ = 18 miles/hour}[/tex]We can conclude that the correct answer is 18 miles/ hour.
