One way in which to evaluate 3 4/6 + 2 5/6 is to add the integers 3 and 2 first and the fractions 4/6 and 5/6 second:
5 9/6.
Next, the improper fraction 9/6 must be rewritten as 3/2 and this 3/2 rewritten as 1 1/2, which in turn is added to that integer, 5:
5 9/6 = 5 + 1 3/6 = 5 + 1 1/2 = 6 1/2 (answer)