Answer: Puedes (poder)
Explanation:
The full sentence is:
"400 euros! No puedes gastar ese dinero en ropa."
The English translation for the question would be:
"400 euros! You ___ waste that money on clothes."
Poder is the best word to use in this sentence. "Devolver" means "to return/to give back". "Poder" usually means "to be able to do something".
The best use of "poder" in this sentence is "puedes", meaning "you can".
"No puedes" means "you can't".
So, the whole sentence would be translated as: "400 euros! You can't waste that money on clothes."
Hope this helps!