Answer:
![x = 16.6\ cm](https://img.qammunity.org/2020/formulas/mathematics/high-school/5cwi8mbkd8topa70w9i4ivekcdsn7vcu8a.png)
Explanation:
To answer this question use the secant line theorem.
If two secant segments are drawn towards a circle from an outer point, then the product of the length of the secant segment y and the length of its outer secant segment is equal to the product of the length of the other secant segment and its external secant segment.
This is:
![(12+6)*6 = (5+x)*5](https://img.qammunity.org/2020/formulas/mathematics/high-school/6ljcan7j7jsx88g715ffww2lwsmj2p0r25.png)
Now we solve the equation for the variable x
![18*6 = 5*5+x*5](https://img.qammunity.org/2020/formulas/mathematics/high-school/ayg69ky8fq89ftmnd120a5wfd1k0vkumuf.png)
![108 = 25+5x](https://img.qammunity.org/2020/formulas/mathematics/high-school/vdqa9x42x2klzwsn3z7aw8mdlwfc2g50m7.png)
![5x = 108-25](https://img.qammunity.org/2020/formulas/mathematics/high-school/6zp4b6k0cuzqlu8u5rpuor9z2ianlkhua7.png)
![5x = 83](https://img.qammunity.org/2020/formulas/mathematics/high-school/qcking1oht9tj5okqbtezsjddv81a33ubi.png)
![x = (83)/(5)](https://img.qammunity.org/2020/formulas/mathematics/high-school/dn35kzmgp9zis32u0kpmm17jfvn2t83mb6.png)
![x = 16.6\ cm](https://img.qammunity.org/2020/formulas/mathematics/high-school/5cwi8mbkd8topa70w9i4ivekcdsn7vcu8a.png)