Given there are 60 minutes in an hour, we can set up an equation:
35 + 40 = 75
75 minutes converts to an hour and 15 minutes, so we can add this to the sum of hours:
2 + 3 = 5 hours
5 hours + 1 hour & 15 minutes = 6 hours & 15 minutes.
Hence, 2hrs & 35 minutes + 3hrs & 40 minutes = 6hrs & 15 minutes.