Angle AOD is a central angle subtending arc AD. Thus, arc AD = 38 degrees.
Angle ABD is an inscribed angle subtending arc AD. Therefore, angle ABD = 38/2 = 19 degrees.
Since AC is a diameter, angle ABC is a right angle (90 degrees). In triangle ABC, angle ACB = 90 - angle ABC = 90 - 19 = 71 degrees.