so if the height is going to be 20ft, that means 20 = 2+35t-16t²
[tex]\bf 20=2+35t-16t^2\implies 16t^2-35t+18=0
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\textit{now, it doesn't factor in integers, thus}
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\textit{quadratic formula}\\\\
x= \cfrac{ - {{ b}} \pm \sqrt { {{ b}}^2 -4{{ a}}{{ c}}}}{2{{ a}}}\implies t=\cfrac{-(-35)\pm\sqrt{(-35)^2-4(16)(18)}}{2(16)}
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t=\cfrac{35\pm\sqrt{73}}{32}\implies t\approx
\begin{cases}
1.361\\
0.828
\end{cases}[/tex]