\( x^{2}-15 x+54=0 \)

Step 1 ：\(x = \frac{-(-15) \pm \sqrt{(-15)^2 - 4 \cdot 1 \cdot 54}}{2 \cdot 1}\)

Step 2 ：\(x = \frac{15 \pm \sqrt{225 - 216}}{2}\)

Step 3 ：\(x = \frac{15 \pm \sqrt{9}}{2}\)