A man is 30 years older than his son. In three years, his age will be twice the age of his son. The present age of his son is:
Choose the correct choice from the following answers:  A) 20  B) 21  C) 27  D) 23  E) 24

Rationale: "let the son ' s present age be x years . then , man ' s present age = ( x + 30 ) years . ( x + 30 ) + 3 = 2 ( x + 3 ) x + 33 = 2 x + 6 x = 27 . answer : c"
Answer: C