Answer
$t=180$
Work Step by Step
$\mathrm{Given:}\:\:\:$ 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:
$60=\frac{1}{3}\cdot t$
$\Rightarrow\: t=60\cdot 3$
$\Rightarrow\: t=180$
