Hey there!
For this question, you are finding how many brownies can be made. You need 1/4 cups of sugar to make ONE brownie. You have 13/4 cups of sugar. Since you have the same denominators, you can ignore them. So it’s basically 1 cup of sugar for a brownie and you have 13 cups. Take 13 and divide it by 1, and it will give you 13 brownies!
Hope this helps!
-Soul