Variables and Expressions

today in math our class started chapter 8. chapter 8 is about Variables and Expressions. and example is n + 9 = 39 you would solve that by doing this n+ 9 + (-9) = 39 + (-9) = 30. How i got that was 9 + (-9) it is negative because the other nine is positive. and what you have to do to the one side you have to do to the other side. so i got that by going 39 from the original question and adding the -9 to it. but you really just have to cancel them out and got your answer to be 30!