The number of hours of daylight in a town changes at a rate of $\dfrac{1}{20}\cos\left(\dfrac{t}{60}+2\right)$ hours per month (where $t$ is the number of days since January $21^{\text{st}}$). **By approximately how many hours does the daylight increase between $t=240$ and $t=300$?** [[☃ radio 1]] [//]: (http://aa.usno.navy.mil/data/docs/Dur_OneYear.php)