Final answer:
Angle ACB measures 140 degrees
Step-by-step explanation:
Given that angle DCA measures 40 degrees, we can use the fact that angles in a triangle add up to 180 degrees to find the measure of angle ACB. In triangle ACB, angle DCA is one of the angles, so we subtract 40 degrees from 180 degrees to find the remaining angle.
180 degrees - 40 degrees = 140 degrees
Therefore, angle ACB measures 140 degrees.