The difference between 31 and 28 is: 
The difference between 73 and 13 is: 
The difference between 39 and 28 is: 
The difference between 31 and 20 is: 
The difference between 71 and 28 is: 
The difference between 31 and 18 is: 
The difference between 34 and 21 is: 
The difference between 31 and 28 is: 