A waiter had 16 customers. After some more arrived he had 38 customers. How many new customers arrived?
The waiter had 16 customers. 
Then, some more arrived. 
Now, the waiter has 38 customers. 

We want to know how many new customers arrived. 

We can solve this problem by finding the difference between the final number of customers and the initial number of customers: 

38 customers - 16 customers = 22 new customers