If (x + y)^2 = 100 and (x - y)^2 = 16, what is the value of xy?
If the question does not specify plus/minus when square-rooting, could have there been more than one correct answer???
While there are more than one solution for x and y separately, all the solutions lead to the same value of xy.
But you don’t have to worry about that. Since it is a grid-in, the possibility exists that there is more than one right answer. As long as you have found one of them, you are fine. So if you play with numbers and discover that x=7, y=3 is one possible solution set, go with it.