Tetsu Rides His Bicycle X Miles the First Day, Y

Tetsu rides his bicycle x miles the first day, y miles the second day, and z miles the third day. Which of the following expressions represents the average number of miles per day that Tetsu travels?

A) x + y + z
B) xyz
C) 3( x + y + z)
D) 3( xyz)
E) ( x + y + z) /3