Thank you, clarkjd, for your thoughtful response.

Dogman_1234, I'm sorry to inform you that the answer is not 2.

What must be considered here is the range of the square root operation. I did not understand that the square root symbol implies that the radical is to be solved *only for the principal square root.* This means that the range of the radical, when solved, is [0, ∞). No input value, x, will produce an output of -4. Therefore, x=4 is not a solution.