to think very hard or for a long time about sth :
She racked her brains, trying to remember exactly what she had said.
to think very hard or for a long time about sth :
She racked her brains, trying to remember exactly what she had said.
Oxford Advanced Learner's English Dictionary. Оксфордский английский словарь для изучающик язык на продвинутом уровне. 2005