First change the mixed fractions into improper fractions. Do this by multiplying the denominator by the whole number, then adding that to the numerator, leaving the denominator the same.
5/4 + 3/2
Now change the fractions so that they have a common denominator. Here, you can use 4 as the CD, so leave the first fraction alone and just change 3/2. 3/2 = 6/4