Lucy went to the grocery store. She bought w packs of cookie and x packs of cake. How many more packs of cookie did she buy over cake?
We know that Lucy went to the grocery store and she bought w packs of cookies and x packs of cake. We also know that she bought more packs of cookies than cake. 

That means that w > x. 

We can solve this problem by subtracting x from both sides. 

w - x > x - x

w - x > 0

That means that w - x is the answer, which is the number of more packs of cookies Lucy bought over cake.