In order to get the letter z by its self you have to do the same thing to each side of the greater or equal to symbol.
In order to get the z by its self you need to do the opposite as what is shown so you can get down to just the simpiest form: for example if you are multiplying you would end up deviding on both sides of you sign.
So insted of dividing z by -8 we will multiply -8 to each side and so on... I will write it out to show you:
