According to the given values, we should use the COSINE ratio to find the missing side. This once we have found the missing angle.
To do it we can use sine ratio and the given values of the opposite side and the hypotenuse:
[tex]\begin{gathered} \sin x=\frac{12}{24} \\ \sin x=0.5 \\ x=\sin ^{-1}0.5^{} \\ x=30 \end{gathered}[/tex]The missing angle measures 30°.