Help with Countifs

[newbielondon123]

Hi Folks,

Need some help with a Countifs on excel.

I want to count the number of quantity of each size of product the specific sales persons have sold.

At the moment I have only gone as far as counting how many Smalls, Mediums, Larges each sales person has sold using the =COUNTIFS(D:D,"Large",F:F,"Alex") But have not been able to add the quantity of each product- would really appreciate some help?

I have attached a sample working data