Answer:
There is only one zero pair added i.e. 9.
Step-by-step explanation:
Given : Function 
To find : How many zero pairs must be added to the function in order to begin writing the function in vertex form?
Solution :
Converting the given function into vertex form,

Adding and subtracting square of 3,

Square form as 


So, The required vertex form is 
There is only one zero pair added i.e. 9.