\(t = 2\) seconds

\begin{align}
&\begin{aligned}
h&=40 t-5 t^{2} \\
60&=40 t-5 t^{2}
\end{aligned}\\
&\begin{aligned}
5 t^{2}-40 t+60&=0 \\
5\left(t^{2}-8 t+12\right)&=0 \\
5(t-2)(t-6)&=0 \\
\end{aligned}\\
&\therefore t=2 \text { or } t=6\\
&\therefore t=2 \text { seconds } \\
\end{align}