It was 3: 45 when you started mowing the lawn. you finished at 4: 30. how long did it take you to mow the lawn

When working with time treat it like a math problem and remove the , : ,
So to find out how long it was from 3:45 to 4:30 it would be set up like a usual subtraction problem with 3 digits.

430 
-345

Which would be: 85 minutes total.
If you wanted the amount of hours, you would just substract 60 in this case, since there's only one hour in the total 

85-60 : Would equal 25, and if you add back the 60 , it would be 1 hour and 25 minutes.