The given triangle has a right angle, which means it is a right triangle.
The ratio of the right triangle sides are related to the functions sine, cosine and tangent. In this case, the angle we want is adjacent to a leg of measure 12 and we know that the hypotenuse of the triangle is 17. This means we can use the cosine of the angle:
Now, taking the arccos, we get:
Which corresponds to alternative D.