Interpreting Function Notation, Graphs, and Context

The amount of garbage, $G$, produced by a city with population $p$ is given by $G=f(p)$. Variable $G$ is measured in tons per week, and $p$ is measured in thousands of people.

The town of Tola has a population of $40{,}000$ and produces $13$ tons of garbage each week. Express this information in terms of the function $f$.