how do you slove this equation?

Question should perhaps be :-
5x² - 7 = 9
5x² = 16
x² = 16 / 5
x = ± 4 / √ 5

well it says to use commm AS NEEDED. so i think you are only suposed to have one anwser which would be 3.2 because:
5x-7=9
add 7 to each side
5x=16
divide each side by 5
x=3.5 so your anwser would be (3.5)

i also think only 1 anwser because you only have one variable (x)

5x-7=9
5x=16
x = 16/5

There is only one answer. "Use comma to separate answers as needed" just means that if you have more than one answer, you need to use a comma to separate the values. Since you only have one answer, no comma is needed.

It only has one answer, so you DON'T need commas.

5x - 7 = 9
5x = 9 + 7
5x = 16
x = 16/5
x = 3 1/5 (3.2)