You can solve this by setting up ratios that when cross-multiplied cancel out the units. For example, having a value with a unit of miles in the numerator and seconds in the denominator multiplied by a value with a unit of seconds in the numerator and minutes in the denominator would cancel out the seconds and leave you with a ratio of miles over minutes.
*You can convert seconds to minutes (if seconds was on the bottom of a fraction) by multiplying by the number of seconds in a minute over one minute.*
Multiply the numerators and denominators separately, cross out canceled units, and simplify if needed. "Crossed out" units are in italics. Units that are kept are in bold.
2+(1/3) miles x 60 seconds x 60 minutes = 8400 miles
1 second 1 minute 1 hour 1 hour
8400 miles per hour