A boy gets 3 marks for each correct sum and loses 2 marks for each incorrect sum. He does 24 sums and obtains 37 marks. What was the number of correct sums?

• A.  \[20\]                                  
• B.                         \[17\]                                  
• C.                         \[31\]                                                  
• D.                         \[19\]