Well, to add fractions, you need to find a common denominator. In this case, the smallest common denominator would be 12. So you must multiply each fraction so that both denominators are 12.
3/4*3/3=9/12
1/3*4/4=4/12
Add those two fractions together, reduce if possible, and you have your answer!
9/12+4/12=13/12
You can't reduce, so 13/12 is your answer.
Hope it helps!
-Lacy