## Thomas' Calculus 13th Edition

When $s$ is $60$, $t$ is equal to $180$.
$s=c*t$ $s=25$ $t=75$ $c=\frac{s}{t}=\frac{1}{3}$ Therefore, when $s=60$ $s=c*t$ $60=\frac{1}{3}t$ $t=180$