report builder 3, parameter difficulty

Hello, I'm having some difficulty establishing a parameter in my report.

My report works currently and people can select multiple DeptID's before running the report.

However, I want to take it one step further and can't get it to work. Each of these DeptId's is associated with a Company. I want people to select a Company, but I want the DeptID's to be brought into the report. Can't figure it out..

Any suggestions?

I have the parameter created so that people can select which company they need. I also have a dataset that shows which depts are associated with which companies, in this format:

Dept / Company 1121 / A 1132 / A 2122 / A 3122 / B etc...

Any help would be greatly appreciated. Thanks