From the question,
[tex]5x=7x-18[/tex]
This is because of the two tangent theorem, which states that if we draw two lines from the same point which lies outside a circle, such that both lines are tangent to the circle, then their lengths are the same.
Therefore,
[tex]\begin{gathered} 5x-7x=-18 \\ -2x=-18 \\ x=\frac{-18}{-2} \\ x=9 \end{gathered}[/tex]
The value of x is 9
