check the picture below. So the rocket reaches its height at its vertex.
the rocket is being launched from the ground, and therefor its initial height is 0, thus
\end{cases}
\\\\\\
h(t)=-16t^2+352t+0 " src="

so we can get the vertex coordinates by using its coefficients, how many "t" seconds will it take? well, that'd be the x-coordinate of its vertex.
