lookup with a dropdown list

[LegoMason]

Hello,
I have a table that shows the list of items, the categories of each item and the number of items sold in a given month.

I would like to create a lead sheet which sums the categories by month. I'd like it to be dynamic and have the month in the drop-down list to allow the user to change to show the data for the month.

how do i write this formula?

 

[ETAF]

a sample sheet would help
so we can see the data layout

 

[jonreeves1975]

here is the file
thanks so much!

 

[ETAF]

try
=SUMPRODUCT(($K$1:$O$1=B$2)*($K$2:$O$14)*($J$2:$J$14=A4))