Final answer:
Angle BAC in a right-angled triangle ABC must be the right angle, which measures 90°, irrespective of the other given angle AD or the length of side AC.
Step-by-step explanation:
The question asks for the measurement of angle BAC in a right-angled triangle ABC where AD measures 30° and AC is given as 10 cm. Since the triangle is right-angled, and considering the convention of naming triangles, angle BAC must be the right angle, that is, 90°. However, the given angle AD of 30° does not seem relevant to finding the measure of angle BAC, especially as the position of point D is not specified within the triangle. The essential understanding here is that in a right-angled triangle, the right angle is always 90°, which is option (b).