This isn't really a problem, but I need to understand what happened here. I was looking at an example and got confused by one of the steps. I can't figure out how to type it here, so all I can say is that it is on page 104 of the Holt Physics Problem Workbook, and it is going from just after it substitutes the continuality equation for v2 to the next step that confuses me. I am so sorry for the lack of information. Thank you for your time.