Answer:
x = 6
Explanation:
These triangles are similar shapes. They have the same shape but different sizes. This means there exists a scale factor between side lengths of the two triangles. They are related. You can find a missing side length by writing a proportion between the sides of each triangle.
![(x)/(x+2)=(9)/(12)\\ 12(x) = 9(x+2)\\12x = 9x + 18\\3x = 18\\x = 6](https://img.qammunity.org/2020/formulas/mathematics/middle-school/r6tkkxnp1p60lviq8rdf1xte7nog7k6ds4.png)