Incorrect: this does not describe a proportional function because y does not equal a constant times x. For example, when $\displaystyle{x}={1},{y}={3}={3}\cdot{1},\usepackage{cmbright}\Huge\$ but when $\displaystyle{x}={2},{y}={12}={6}\cdot{2}.\usepackage{cmbright}\Huge\$