Determine the Set of Values of X for Which the Radical

Multiple Choice

Determine the set of values of x for which the radical expression would produce a real number.
- $$\sqrt { 15 - x }$$

A) $\{ x \mid x \leq 15 \}$
B) { }
C) $\{ x \mid x > 15 \}$
D) $\{ x \mid x \geq 15 \}$