we have the equation
[tex]h=-16t^2+144[/tex]
Remember that
when the stone hit the ground, the value of h is zero
so
For h=0
[tex]-16t^2+144=0[/tex]
solve the quadratic equation
[tex]\begin{gathered} 16t^2=144 \\ t^2=\frac{144}{16} \\ t=\pm\frac{12}{4} \\ t=\pm3 \end{gathered}[/tex]
the solution is the positive value
t=3 sec
