Chapter 9 - Solving Quadratic Equations - 9.3 - Solving Quadratic Equations Using Square Roots - Exercises - Page 501: 33

$x\approx 1.22$ seconds

$$h=-16x^2+24$$ When hitting to the ground, $h$ becomes zero: $$0=-16x^2+24$$ $$16x^2=24$$ $$x^2=\frac{24}{16}=\frac{3}{2}$$ $$x=\pm\sqrt{\frac{3}{2}}\approx \pm 1.22$$ Take the positive value: $$x\approx 1.22\text{ seconds}$$