The total of thirteen numbers = 13X9 = 117
The total of first 6 and last 6 numbers is = 6 X 5+6 X 7 = 72
So, the middle number is (117 - 72 ) = 45
The average of thirteen numbers is 9. The average of first six numbers is 5 and the average of last six numbers is 7. What is the middle number?

a: 47
b: 45
c: 25
d: 37
e: 44