Answer: The correct answer is 60.
Step-by-step explanation: There are a couple of pieces of data that you need to know in order to answer this question. First, the total of all interior angles of any triangle is 180. Second, a triangle has 3 interior angles. Third, the mean is defined as the average.
In order to solve this problem you will need to divide 180 (total of all angles) by 3 (number of angles) which equals 60. This is the mean of the angles of a triangle.