If the average (arithmetic mean) of \(x\) and \(y\) is \(60\) and the average (arithmetic mean) of \(y\) and \(z\) is \(80,\) what is the value of \(z-x?\)
A. 70
B. 40
C. 20
D. 10
E. It cannot be determined from the information.
Answer: B
Source: Official Guide