m is the input (mth month of 2012) with months as units. A is the output with thousands of tourists as units. This is a function.
Work Step by Step
We know that m is the input because it is inside the parentheses. A is the output because it is the "coefficient" of the parentheses. The units of months and thousands of tourists are both given in the problem. This is a function because there can only be one quantity of tourists that come to Arizona during any month.