is that a question on a test? If so, then the textbook will also provide you the information how to calculate this.
As trainers, we often need to go on a quest for an answer, read information from multiple sources and then come up with the answer that is right for us. During that process, we learn a lot on the periphery that often comes in handy for the next situation. While it is tempting to just have somebody else give you the answer, it is a lot less valuable.