Create a Measure to Count based on a condition

Hi,

So i have a PowerPivot and i need to create a Measure to count the values based on a specfic value that is in the column and also to count only items that fall under certian category. So basically it is Countif function but am stuck here. I have done only Count function but how do i insert the if condition part here 

so i have the above data and i have created a measure called 'Bill Rate Over Max'

I now want this measure to count all the workers that has 'Bill Rate Over Max' which i have done as shown below

=calculate(count(EDE[Worker]),EDE[Max over Bill Rate?]="Bill Rate Over Max")

But now i want to add another condition which is if the 'Invoice Option' is "Staffing" it has to give the result for the same. For now this formula is calculating values for workers on