If , then x is equal to

We have

We know that determinant of A is calculated as

⇒ x(x) – 2(18) = 6(6) – 2(18)

⇒ x² - 38 = 36 – 38

⇒ x² =36 – 38 + 38

⇒ x² = 36

⇒ x = �6