Baker made 21 cakes. He sold 25 of them and bought 14 new cakes. How many more cakes did baker sell than those he bought?
Baker made 21 cakes. 
He sold 25 of them. 
That means he has 4 left. 
He bought 14 new cakes. 
That means he has 18 cakes in total. 

Now we can see that he sold 18 cakes and bought 14 cakes, so he sold 4 more cakes than he bought.