Solve x2 = 12x – 15 by completing the square. Which is the solution set of the equation?

(negative 6 minus StartRoot 51 EndRoot comma negative 6 + StartRoot 51 EndRoot)
(negative 6 minus StartRoot 21 EndRoot comma negative 6 + StartRoot 21 EndRoot)
(6 minus StartRoot 51 EndRoot comma 6 + StartRoot 51 EndRoot)
(6 minus StartRoot 21 EndRoot comma 6 + StartRoot 21 EndRoot)