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\begin{aligned}&y=0+0-\frac{1}{2} g t^{2} \\ &t^{2}=\frac{2 y}{-g} \\ &t \quad=\pm \sqrt{\frac{2 y}{-g}}=\pm \sqrt{\frac{2(-30.0 \mathrm{~m})}{-9.80 \mathrm{~m} / \mathrm{s}^{2}}}=\pm \sqrt{6.12 \mathrm{~s}^{2}}=2.47 \mathrm{~s} \approx 2.5 \mathrm{~s} \end{aligned}