If you are a Leo Messi in English grammar could you help me?

6 years ago

Which one to chose in the 15th 'took' ot 'had taken'? Explain why?  

“At 2 o’clock in the afternoon Mr Gregory was sitting in the reclining chair in the middle of the room. This was his first morning in the new office. He was surrounded by folders they hadn’t managed to arrange on the shelves during the day. It 15) a. took / b. had taken a week to pack all this stuff. He knew that he had to do this himself as his assistant had gone on holidays. She was going to return in a week.”

Thank you very much!