Hi there! :)
Answer:
20% of the money she saved last year was saved during the month of January.
Explanation:
Marie saved $3,000 last year.
She saved $600 in the month of January.
SO, Marie saved:

In order to answer your question, you'll need to use the cross product method (because you want to have a percentage, which is on 100 and not on 3,000 like we have right now):

(100 × 600) ÷ 3,000 = x
60,000 ÷ 3,000 = x
20 = x
There you go! I really hope this helped, if there's anything just let me know! :)