Our goal is to have v on one side and the rest on the other side of the equation. The key is to keep the balance, what-ever we add/divide/multiply/subtract on one side, we /divide/multiply/subtract on the other side as well. This is because, say, if you had five coins on one hand and five on the other, then you can say that the number of coins in your left hand is equal to the number of coins in your right hand (that is what the ''='' sign means); but if you take one of out of the right hand and nothing on the left, then what you have said about your left-hand coins and right-hand being equal no longer holds (and the the ''='' sign no longer applies)). That understood, the rest is easy.