Answer:
30°
Explanation:
I don't know what you've been taught, but I'll explain how I did it.
Upon looking at this, I thought, "at what angles is cosine √3/2?" Using a unit circle in my head, I thought of π/6 and 11π/6 (which are in radians, in degrees they are respectively 30° and 330°). Since x is acute (less than 90°), the answer must be 30° since that is the only one of the two that is acute.