What is the unit rate to this equation? 346 miles on 22 gallons

Calculating the unit rate is not that problematic if you can understand the requirement. Using the details given the answer to the question can be easily determined.
Number of miles that it goes in 22 gallons = 346
Then
Number of miles that it goes in 1 gallon = (346/22) miles
                                                                = 15.73 miles
So
The unit rate to this equation is 15.73 miles per gallon. I hope the procedure is clear enough for you to understand.You can always use this procedure for solving similar problems in future.