Suppose that the two lines that form the missing angle are tangents to the circle. Then, the measure of the missing angle can be found using the following equation:
![\measuredangle ABC=\frac{arc\text{ AEC - arc AGC}}{2}](https://img.qammunity.org/2023/formulas/mathematics/college/zk48zpgfm0nucvygih3j2zd61xtro4lt28.png)
Notice that we can complete the information about the arcs of the circle with the central angle:
then, we can find the angle x with the following expression:
![\begin{gathered} \measuredangle x=(243-117)/(2)=(126)/(2)=63 \\ \Rightarrow\measuredangle x=63\degree \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/bgy078hkmppxa0fv7tm3s95ty75g1esqvf.png)
therefore, the measure of the missing angle is 63 degrees.