The concept of LCM has to be understood first. When adding two fractions their respective denominators are used to get the LCM. In this scenario the denominators are 3 and 6. The LCM of 3 and 6 is 6. The LCM can be found using the table method or the factors method.
3 = 3 X 1
6 = 2 X 3
LCM = 1 X 2 X 3 = 6
The LCM is then put as the denominator of the answer, fractions are brought to the common denominator:
9/6 is further simplified to 3/2 = 1 +1/2