## University Calculus: Early Transcendentals (3rd Edition)

$t=180$
$\mathrm{Given:}\:\:\:$ The variable $\:s\:$ is proportional to $\:t.$ We can write the above statement as a relation: $s\:\propto\:t$ Let's introdue a proportionality constant $\:k\:$ to turn the relation into an equation as: $s=k\cdot t$ We can find the value of $\:k\:$ when we are given $\:s=25\:$ and $\:t=75.$ $25=k\cdot 75$ $\Rightarrow\: k=\frac{25}{75}=\frac{1}{3}$ So that our general equation $\:s=k\cdot t\:$ becomes: $s=\frac{1}{3}\cdot t$ When $\:s=60,\:$ we have: $60=\frac{1}{3}\cdot t$ $\Rightarrow\: t=60\cdot 3$ $\Rightarrow\: t=180$