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:
because each dimension of A is 3 tomes each dimension of B, that will mean that both the length and width of B are multiplied by 3 in order to get the length and width of A, so the area of B is length×width=162 and the area of A (in terms of B's dimensions) is 3xlength×3×width=9×length×width=9×162=1458 sq cm
