Excel Function return a certain value if citeria x is met

[Cham]

Hi,
I have the following function
=IF(C13=0,(WORKDAY(D13,0)),(WORKDAY(D13,C13-1)))
and I have a column that has "x", which meant it is completed.
I want to write a function that will help me reference the formula so that
if the column does have an x then the above function answer should appear,
otherwise i want it to be blank.

 

[Gary''s Student]

Let's say the column with the x'xs is column X:

=IF(X13="x",IF(C13=0,(WORKDAY(D13,0)),(WORKDAY(D13,C13-1))),"")

 

[Cham]

I used that, it did not work correctly.