To solve this, you need to have a common denominator for both terms. In order to get the equivalent fraction with the common denominator, you multiply each fraction by a version of 1. Here, it seems like our least common denominator (or LCD) is 12. Therefore, you multiply 1/4 by 3/3 and you multipy 2/3 by 4/4 to get 3/12 plus 8/12 = 11/12.
Hope this helps!