Chapter 11 - Quadratic Functions and Equations - 11.8 Problem Solving and Quadratic Functions - 11.8 Exercise Set - Page 755: 33

$f\left( x \right)=mx+b$

In the provided bar graph between purchasing power of one 1985 dollar to the year, it is observed that the data points fall continuously from 1985 to 2015. The graph does not appear to represent a quadratic function that opens upward or downward. Thus, the linear function $f\left( x \right)=mx+b$ can be used to model the data.