That means I want to find a factor or a common factor of five and two. And this factor is ten, because two goes into ten five times, and five goes into ten two times. So I basically multiply this whole guy out by five, and I multiply this whole guy out by two, and I get the following. So five times this guy gives me this, five times this guy gives me this guy five times, two H gives me ten H, and five times this guy gives me ten electrons. I multiply this whole guy by two. I get two of these guys plus 16 of H pluses plus ten of east equals two of these guys and eight of these guys.