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?
First, we need to find out how many packs of cookie Lucy bought. We know that she bought w packs of cookie and x packs of cake. This means that she bought w + x packs of cookie. 

Now, we need to find out how many more packs of cookie she bought over cake. To do this, we need to subtract the number of packs of cake she bought from the number of packs of cookie she bought. We know that she bought x packs of cake, so she bought w + x - x packs of cookie. 

This means that she bought w packs of cookie.

Therefore, the answer (symbolic expression) is: 

w