This question is about rearranging the equation so that all the known variables are on one side and all the unknown variables are on the other side. To start with we can look at the x terms, remembering to reverse the signs as you cross them over to the other side. 10x - 15 = 5 Now we do the same with the known variables, so we add 15 to both sides. 10x = 20 To find x on its own, we divide both sides of the equation by 10. x = 2