Using the distance formula: $\sqrt{(x-3)^2 + (-5-(-5))^2} = 15$
$\Rightarrow |x - 3| = 15 \Rightarrow x - 3 = \pm 15 \Rightarrow x = 18$ or $x = -12$
The answer is (b) $-12, 18$.
Source: Distance Formula, Chapter 7, Section 7.2
Since both points have the same y-coordinate (−5), the distance reduces to $|x - 3| = 15$. Solve both cases: $x - 3 = 15 \Rightarrow x = 18$ and $x - 3 = -15 \Rightarrow x = -12$. Watch the order in the options — the correct option lists $-12$ before $18$, which is option (b).