The average of 1st 3 of 4 numbers is 16 and of the last 3 are 15. If the sum of the first and the last number is 21. What is the last numbers? Choose the correct answer.
A) 2  B) 4  C) 9  D) 5  E) 7
A + B + 9 = 48   B + 9 + D = 45   A + D = 21   A – D = 3   A + D = 21   2D = 18   D = 9   ANSWER 9
<result>C</result>
The average of 1st 3 of 4 numbers is 16 and of the last 3 are 15. If the sum of the first and the last number is 21. What is the last numbers?