Track and field. A 100 meter dash in 10 seconds.  How many mph is that ?

22.3694 miles per hour.

Convert meters to miles and seconds to hours then use a conversion calculator.  Every smartphone has one.

or convert meters per second to miles an hour.  

This looks like a homework question, so I don't give you a direct answer. In math, one of the reasons you are given homework questions is to help you develop problem solving skills.

(If this is, in fact, a homework question, you should move it to "Education and Reference > Homework Help.)

For your answer, you want speed. Speed is measured in distance / unit time. 

You have distance / 10 units of time, in this case seconds. If the sprinter runs 100 meters in 10 seconds, what distance will he run in 1 second? (Average.)

Now, you have a unit time, but it isn't the unit you want. You have seconds, you want hours. How many seconds are in 1 hour? 

Doing those 2 steps, you can get meters / hour. For the last step, you have to convert the meters to miles.