Trees in 5 rows with 4 in each row puzzler

Although this was a puzzler from a very long time ago, I would just like to inform everyone that I am not the best in maths class but having heard the answer to this puzzler, I was put at the top of class. My teacher handed out some problems and it took me only twi seconds to write down the answer thanks to Car Talk! Thank you Tom and Ray!! :smiley: