Hey there!
GUIDE for you to follow:
1 week = 7 days
SO POSSIBLY
3 weeks = 21 days (because 3 * 7 = 21)
SOLVING for your answer
3(7) + 4
= 21 + 4
= 25
ANSWER
Therefore, the answer is most likely
25 days old
Good luck on your assignment & enjoy your day!
~Amphitrite1040:)