In seventeen given numbers, the average of first 9 numbers is 4 and that of the last 9 numbers is also 4. If the average of these 17 numbers is 3, the 9th number is Choose one.
A) 23  B) 4  C) 17  D) 21  E) 28
Explanation :   9th number = (9*4 + 9*4 - 17*3)= 
<gadget id="calculator">(9*4 + 9*4 - 17*3)</gadget>
<output>21</output>
21.   Answer : 21
<result>D</result>
In seventeen given numbers, the average of first 9 numbers is 4 and that of the last 9 numbers is also 4. If the average of these 17 numbers is 3, the 9th number is