You solved the equation $\displaystyle{5}=-{16}{{t}}^{{2}}+{25}{t}+{5}\usepackage{cmbright}\Huge\$ , when you should have solved the equation $\displaystyle{0}=-{16}{{t}}^{{2}}+{25}{t}+{5}\usepackage{cmbright}\Huge\$ . The question asked when the ball would hit the ground, not when it would be back to the height it was thrown from.