If the average (arithmetic mean) of a and b is 50 and the average of b and c is 70, what is the value of c − a?	Choose the correct option.
A) 40
B) 50
C) 90
D) 140
E) It cannot be determined from the information given.
-(a + b = 100)   b + c=140   c-a=40   40.40
<result>A</result>
If the average (arithmetic mean) of a and b is 50 and the average of b and c is 70, what is the value of c − a?