$$z = \pm3$$
Work Step by Step
First you add 45 to both sides $$5z^2 = 45$$ Then you divide both sides by 5 $$z^2 = 9$$ Then you find the square root of both sides $$z = \pm3$$ That is your final answer since the variable is alone now. Remember you always have to put the plus or minus sign ($\pm$) because any number under the square root that is above $0$ has $2$ has answers. And you can multiply the negative version of the number by itself to get the number that is under the square root.