@Yacchan
google could've done it for you but here is a link to the merrium Webster dictionary showing that "quick study" is a noun, just like it's used in this chapter.
https://www.merriam-webster.com/dictionary/quick%20study#:~:text=%3A%20one%20that%20can%20speedily%20learn%20the%20essentials%20of%20something%20to%20be%20done
google could've done it for you but here is a link to the merrium Webster dictionary showing that "quick study" is a noun, just like it's used in this chapter.
https://www.merriam-webster.com/dictionary/quick%20study#:~:text=%3A%20one%20that%20can%20speedily%20learn%20the%20essentials%20of%20something%20to%20be%20done
check out my 19 days fanfic on ao3 :)