Since there is 120 minutes in 2 hours, you would divide 4/120 which would be simplified to 1/30. Therefore, the parade traveled 1/30 miles per minute or 0.03(a bar notation on 3) miles per minute.
There's a really easy way to convert any units to other units.
Right now, we have the fraction (4 miles) / (2 hours).
We want to find a fraction that's exactly equal to that one, but has the units of (miles/minute) or maybe (feet/minute).
Just take the original fraction, and multiply it by some other fractions.
Each fraction you multiply it by must have the value of ' 1 ' so you don't change the value of the original fraction. But it can have different units, that cancel with other units to eventually give you the units you want.
(4 miles / 2 hours) times (1 hour / 60 minutes)
The second fraction is equal to ' 1 ', because the top and the bottom have the same value ... 1 hour is the same thing as 60 minutes.
Multiply the fractions: (4 miles x 1 hour) / (2 hour x 60 minutes)
Now you can cancel 'hour' from the top and the bottom, and you have