$p(t)=175+2.5t$ (in thousands of people), where $p(t)$ is the population of the country and $t$ is the amount of years since $2008$.
Work Step by Step
In the equation $p(t)=at+b$: The rate of change (in population), $a$, is $2,500$ people every year. The initial output, $b$, is $175,000$ people. Rewrite this as $p(t)=2,500t+175,000$, or simplify it to $p(t)=2.5t+175$ (in thousands of people).