A balloon is catapulted into the air from the top of a building. The height $h(t)$ in meter of the ballon after $'t'$ seconds is $h(t) = -5t^2 + 30t +10$. When will the balloon reach a height of 30 m ?

Question

$\begin{array}{1 1} (a)\; \text{5 seconds} \\ (b)\; \text{6 seconds } \\ (c)\; \text{3 seconds } \\ (d)\; \text{2 seconds} \end{array}$