the denominators must be the same so, since 4 goes evenly into 24 we can create an equivalent fraction from 3/4 to 18/24 (multiply numerator and denominator by 6)
now you can add:
+ = =
since the numerator is larger than the denominator this is called an improper fraction and can be changed into a mixed number by dividing 24 into 33
24 goes into 33 one time with a remainder of 9
so 33/24 = 1 wherein 9 and 24 can each have a 3 factored out to make it fully simplified