Hi Sydney,
To answer this question, you need to find out how many people are in the entire class, since they are asking what percentage of the class are boys.
So add the girls and boys up and you have your class size total.
Now take the number of boys (6) and divide it into the total class size number (24) to get the percentage. I don't want to give you the answer directly, but the hint I'll give is that (provided you're in the US), it's a commonly used larger coin that you can get 4 of when getting change for a dollar. :)
Hope this helps and good luck!