We have the next quadratic function
[tex]f(x)=-16x^2+64x+5[/tex]
The question give us f(x)=10ft
[tex]\begin{gathered} 10=-16x^2+64x+5 \\ -16x^2+64x+5-10=0 \\ -16x^2+64x-5=0 \end{gathered}[/tex]
so we will use the formula to solve quadratic functions
[tex]x_{1,2}=\frac{-b\pm\sqrt[]{b^2-4ac}}{2a}[/tex]
where
a=-16
b=64
c=-5
we substitute the values
[tex]x_{1,2}=\frac{-64\pm\sqrt[]{64^2-4(-16)(-5)}}{2(-16)}[/tex]
[tex]x_{1,2}=\frac{-64\pm\sqrt[]{4096-320}}{-32}_{}[/tex][tex]undefined[/tex]
