You must use this formula:

Where "d" is the distance, "r" is the rate and "t" is time.
If you solve for "r":

If you solve for "t":

Knowing that Joe runs 3 mile in 42 minutes, you can find "r". Notice that:

Then:

Knowing the rate, you can set up the following in order to find the time in minutes it takes Joe to run a mile:

Substituting values into the formula for calculate the time, you get:

The answer is: It takes him 14 minutes to run a mile.