7.5. 15. 30. None of the choices are correct.

Answer:
15
Step-by-step explanation:
Since we are given 2 sets of angles, we can determine the 2 triangles as congruent using AA Congruence Theorem. So if mAB = 15, then mCB also equals 15.
Step-by-step explanation:
∠ABC forms and Obtuse angle ( A measure greater than 90° but less than 180°)
mAB is 90° and mCB is 30°
If AB = 15, then CB must be 12.
[tex]\frac{180}{15} = 12[/tex]