For this case we have the following:
1 word for 5 seconds
2 words for 10 seconds
3 words for 15 seconds
4 words for 20 seconds
5 words for 25 seconds
6 words for 30 seconds
7 words for 35 seconds
and so on, successively, until you reach 12 words in 60 seconds
It is observed, that Casey takes 5 seconds to write a word.
When he has written 5 words, it takes 25 seconds.
Answer:
5 words for 25 seconds
