It is in the air 5.625 seconds.
Using the quadratic formula,
[tex]t=\frac{-b\pm \sqrt{b^2-4ac}}{2a}
\\
\\=\frac{-90\pm \sqrt{90^2-4(-16)(0)}}{2(-16)}
\\
\\=\frac{-90\pm \sqrt{8100-0}}{-32}
\\
\\=\frac{-90\pm \sqrt{8100}}{-32}=\frac{-90\pm90}{-32}
\\
\\=\frac{-90+90}{-32}\text{ or }\frac{-90-90}{-32}=\frac{0}{32}\text{ or }\frac{-180}{-32}
\\
\\=0\text{ or }5.625[/tex]
0 is when the ball is first launched, 5.625 is when it hits the ground again.
