If the average (arithmetic mean) of a and b is 40 and the average of b and c is 60, what is the value of c − a?	Select the correct option
A) 25  B) 40  C) 90  D) 140  E) it can not be determined from the information given .

Rationale: "- ( a + b = 80 ) b + c = 120 c - a = 40 b . 40"
Answer: B