Since all your denominators are the same all you have to do is add them together.
 2 1/4 
 4 1/4 First bring down your denominator 4, now add you numerators which 
+ 3/4  3 + 1 + 1 = 5. Now add your whole numbers 2 + 4 = 6. Now you have 
 6 5 /4 6 5/4 which is an improper fraction so you have to divide 5 ÷ 4 and you 
 come out with 1 1/4. Since the 1/4 is already simplified, just 
 add that 1 + 6 = 7 and you have the 1/4. Your answer would be 7 1/4.
6 5/4 = 7 1/4
Hope I was able to help you understand. :-)