Let’s say I have a company that has 2019 revenues of USD 10 million and EUR 20 million. If I want to sum these revenues in USD, what is the right way to do it?

Do I use EUR/USD rate as of 31/12/19? Do I use today’s rate? Or the average of 2019? 

What is the “correct” way that you would tackle that in practice? My objective is to value the company and to do that I want to have a sum of revenue, profit etc. in a single currency (USD).