Incorrect. Since you are interested in finding the maximum height of the marble, you only need to find the vertex of the parabola. Starting with the equation $\displaystyle{h}=-{16}{{t}}^{{2}}+{v}_{{o}}{t}+{h}_{{o}}\usepackage{cmbright}\Huge\$ , substitute in the values for initial velocity and starting height to obtain $\displaystyle{h}=-{16}{{t}}^{{2}}+{32}{t}+{15}\usepackage{cmbright}\Huge\$ . Then rewrite as $\displaystyle{h}=-{16}{\left({{t}}^{{2}}-{2}{t}\right)}+{15}\usepackage{cmbright}\Huge\$ . Can you complete the square so that you can find the vertex form $\displaystyle{y}={a}{{\left({x}-{h}\right)}}^{{2}}+{k}\usepackage{cmbright}\Huge\$ ?