Suatu zarah bergerak di sepanjang suatu garis lurus dan melalui titik tetap $O$. Sesarannya, $s$ m, dari $O$ diberi oleh $s = 2t^3 - 21t^2 + 60t$, dengan keadaan $t$ ialah masa, dalam saat, selepas melalui $O$. Cari masa, dalam saat, apabila zarah itu berhenti seketika.

A particle moves along a straight line and passes through a fixed point $O$. Its displacement, $s$ m, from $O$ is given by $s = 2t^3 - 21t^2 + 60t$, where $t$ is the time, in seconds, after passing through $O$. Find the times, in seconds, when the particle is instantaneously at rest.