given the equation,
h = 4 + 23t - 16t^2
given h = 12
12 = 4 + 23t - 16t^2
lets take everything to the left
16t^2 - 23t + 12 - 4
16t^2 - 23t + 8
lets use formular methos to solve the equation
[tex]x\text{ = }-b\text{ }\pm\frac{\sqrt[]{b2\text{ - 4ac}}}{2a}[/tex]
let t = x
a = 16
b = 23
c = 8
so,
[tex]\begin{gathered} x\text{ = -(-23) }\pm\sqrt[]{(-23)\frac{-4(16)(8)}{2(16)}} \\ =\text{ 23 }\pm\text{ }\sqrt[]{529\frac{-512}{32}} \\ =\text{ 23 }\pm\sqrt[]{\frac{17}{32}} \\ \text{therefore,} \\ t=\text{ 23 + }\sqrt[]{\frac{17}{32\text{ }}}\text{ or 23 -}\sqrt[]{\frac{17}{32}} \end{gathered}[/tex]