Polynomial Long Division

The total number of passengers at the $30^{\text{th}}$ Street Station in Philadelphia on January $5$ from $6:00$am to $8:00$pm can be modeled by the function $f(x)=5x^{2}+21x+18$. The total number of trains that left the station can be modeled by the function $h(x)=x+3$. If $x$ is the number of hours since $6:00$am, on average, how many passengers were on each train at $5:00$pm?