For this case we observe that the first table has a constant rate of change. 
 In linear functions, the rate of change is constant. 
 To prove it, we will find the rate of change for two different intervals. 
 Interval 1: 
 
 
 
 
 
 
 
 
 
 Interval 2: 
 
 
 
 
 
 
 
 
 
 
 
 
 Since the rate of change is constant, then the function is linear. 
 Answer: 
 The first table is a linear function.