31 storks and 35 birds were sitting on the fence. 17 more birds came to join them. How many more birds than storks are sitting on the fence?
There are 31 storks and 35 birds sitting on the fence. 
17 more birds came to join them. 

Now we have 31 storks and 52 birds sitting on the fence. 

There are 21 more birds than storks sitting on the fence.