how fast is this? 12.50 miles in 29 minutes?

Well it is 

$$\frac{12.5\:miles}{29\:minutes}\\\\
=\frac{12.5}{29}\frac{\:miles}{\:minutes}\\\\
=0.431034482\: miles/minute$$

Now, maybe you want to know what that is in miles/hour?

Well there are 60minutes in an hour and you'll go a lot further in an hour than in a minute so it must be multiply

$$=0.431034482*60\: miles/hour\\\\
\approx\:25.86206897\: miles\: per\: hour\\\\
\approx\:25.9\: miles\: per\: hour \mbox{ correct to 1 dp}$$