Make certain that you write both fractions with the same denominator.    

For instance, if the problem is  4 3/4  +  9 2/5:

Find the common denominator (multiplying them will give you a common denominator) 4 x 5 = 20

To change 3/4:  3/4 x 5/5  =  15/10   (multiply the numerators together: 3 x 5 = 15                                                                                                        and the denominators together: 2 x 5 = 10) 

To change 2/5:  2/5 x 4/4  =  8/20

So the problem becomes:  

    4 15/10  + 9 8/20   =   13 23/20     (Add the numerators together; put that answer over the common                                                                     denominator.)

23/20   =   1 3/20     so     13 23/20   =  13 + 1 3/20     =  14 3/20

I hope this helps. If you have specific questions, please re-pst.