In following number series, two terms have been put within brackets. Choose the appropriate option - 2 , 5 , 9 , 19 , 37 , x

Answer: B. 75

The second number is one more than twice the first ;
third number is one twice second ; 
fourth number is one more then twice  the third ;
fifth number is one less then twice  the fourth.
Thus the sixth number is one more than twice the fifth.