Let's start with day 1:
We know that Joe practiced from 6:30 to 7:05
An hour is 60 minutes
Joe practiced for the 30 minutes left in that hour and 5 minutes into the next
30+5=35
So, he was playing for 35 minutes on the first day
Now, we can do the same thing for the second day:
He started at 3:55 and ended at 4:15
An hour is 60 minutes
Joe practiced for the 5 minutes left in the hour and the first 15 minutes of the next hour
5+15=20
Now we want to add the number of minutes he practiced for both days
35+20=55 minutes