If x - y = z, then which of the following represents the average of x, y and z, in terms of x?

Question: If x - y = z, then which of the following represents the average of x, y and z, in terms of x?

Solution:
Given x - y = z.
Sum of x, y, z = x + y + (x - y) = 2x.
Average = (2x)/3.
Thus, the average is 2x/3