I'm guessing you want a formula to solve this problem...?
The best way to solve this would be in proportions. You have miles over hours like this:
x/y
And then you would have what you're trying to solve for on the other side, and you put them equal to each other:
x/y = a/z
x is the number of miles that you travel in y hours. a is the number of miles you are trying to solve for with the given hour value of z. For example:
Margarita is driving at the speed of 10 miles per hour. The distance Margarita covers in 19.5 hours is a miles. Solve for a.
10/1 = a/19.5
Now crossmultiply:
195 = a