Replace the phrase in bold in the following sentence to make the sentence grammatically correct. If the sentence is correct, mark 'No correction required' as the answer. (Ignore the errors of punctuations, if any).
Puneet rack his brains and tried to find an answer to a tricky question given in the paper but couldn’t find one.
racked his brains
The idiom rack your brain/s means: to think very hard or for a long time about something.