What you do is:
Convert 3 2/3 into an improper fraction
Multiplying the whole number to the denominator, of which the total is added by the numerator
The denominator stays the same whilst the numerator is the new total = 11
So it'll be 11/3
Now you see that you must find the sum of 11/3 + 5/4
Find the LCM of both denominators, which 12, multiplying the amount needed to make them twelve to the numerators.
You then get:
44/12 + 15/12 = 59/12
59/12 --> 2 11/12