Final answer:
You can make 15 dozen cookies using all your white sugar.
Step-by-step explanation:
To find the number of cookies you can make using all your white sugar, you need to set up a proportion. Since the recipe calls for (5)/(4) of a cup of white sugar to make 3 dozen cookies, you can set up the proportion:
(5/4) cup sugar / 3 dozen cookies = 25 cups sugar / x dozen cookies
Now, cross-multiply and solve for x
Therefore, you can make 15 dozen cookies using all your white sugar.