Later on in the story (The Necklace), we read that Della lends Mathilda a diamond necklace. Well at the end of the story, the narrator states that the "diamond" necklace was nor real. It was a plaster model. This helps us prove that neither of them are rich and can't afford nice jewelry.
Work: This is just simple multiplication. 4 x _ = 12. If you look at a multiplication table, it's 3. So, it would take 3 minutes to eat 12 sprouts. I hope this helps, and stay safe! :)