Answer:
12
Step-by-step explanation:
By tangent secant theorem intersecting outside of a circle, we have:
[tex] {x}^{2} = 6 \times (6 + 18) \\ {x}^{2} = 6 \times 24 \\ {x}^{2} = 144 \\ x = \sqrt{144} \\ x = 12 \\ [/tex]
