The average of 1st 3 of 4 numbers is 6 and of the last 3 are 5. If the sum of the first and the last number is 21. What is the last numbers?  Choices:
A) 4
B) 5
C) 6
D) 7
E) 9
A + B + C = 18   B + C + D = 15   A + D = 21   A – D = 3   A + D = 21   2D = 18   D = 9   ANSW9R:9
<result>E</result>
The average of 1st 3 of 4 numbers is 6 and of the last 3 are 5. If the sum of the first and the last number is 21. What is the last numbers?