Willis analyzed the following table to determine if the function it represents is linear or non-linear. first he found the differences
in the y-values as 7 - 1 = 6, 17 - 7 = 10, and 31 - 17 = 14. then he concluded that since the differences of 6, 10, and 14 are
increasing by 4 each time, the function has a constant rate of change and is linear. what was willis's mistake?