$An$ emergency flare $is$ shot vertically into the air with a speed $of60\frac{m}{s}.$ It's height $h$

metres after $t$ seconds $is$ given $by$ the equation $h=-5(t-6{)}^2+180.$

$To$ the nearest second, when does the flare reach its maximum height?

After $36s$

After $180s$

After $5s$

After $6s$