Hi helpforpsle, I believe the answer is wrong and perhaps your son has mis-read the question.

There was a decrease in the number of boat rentals this week as compared to last week. So, at first glance, we know that the number of  boat rental this week should be smaller, hence it will be fewer than 450.

Since there was a decrease of 32%, it means that this week, the number of boat rental is only 68% of last week’s boat rentals. 

To solve, 

100% of last week is 450

1% of last week will be 4.5

68% of last week, which is also this week, will be 68 x 4.5, which is 306!

Hope this helps! Feel free to PM me if there is more I can help out with.  I’ve dropped you a pm too. 🙂

Thank you very much