Counting "active" companies

Hi,

my simplified data is as follows:

TABLE1

CompanyID

CompanyName

TABLE2

ProductID

ProductName

ProductCreatedDate

CompanyID

TABLE3

InvoiceNumber

InvoiceDate

ProductID

I know how to find active companies last month based on created products (DistinctCount(CompanyID) where ProductCreatedDate(month) = LastMonth)

I know how to find active companies last month based on sold products (DistinctCount(CompanyID) where InvoiceDate(month) = LastMonth)

But how do I find a count of active companies for a given month, that has sold AND/OR created a product?

Thank you in advance for your help.