Hi Katy,
The division approach is a good way to answer this question. Here's a slightly different approach that might also appeal to your intuition:
- Answers A and C don't make sense, because if we have $0.60 left we could buy another apple
- Answer D doesn't make sense, because we can't buy 21 apples if that leaves us $0.60 short
- That leaves answer B, which is the correct answer
This "process of elimination" approach can be helpful, because it's a really fast way to solve problems if you get the trick.
Best of luck and don't hesitate to be in touch with any further questions,
Viv