A number is doubled and 9 is added. If the resultant is trebled, it becomes 51. What is that number?  Choose the correct choice from the following answers:
A) 3.5 B) 6 C) 8 D) 7 E) 4

Rationale: "let the number be x . then , 3 ( 2 x + 9 ) = 51 2 x = 8 = > x = 4 answer : e"
Answer: E