Out of four numbers ,the average of first three is 16 and that of the last three is 15. If the last number is 18,the first number is :	Choose the correct choice from the following choices.
A) 22  B) 21  C) 77  D) 99  E) 27
Explanation:   Let the numbers be a,b,c,d   Given, a + b + c = 48, b + c + d = 45   Now, d = 18   thus, b + c + 18 = 45 ⇒ b + c = 27   Putting the value of b + c in a + b + c = 48   a + 27 = 48 ⇒ a = 21   Answer: 21
<result>B</result>
Out of four numbers ,the average of first three is 16 and that of the last three is 15. If the last number is 18,the first number is :