A cell phone falls off a balcony. It's height (in feet) is given by the formula
f(x)=16t2+8.6t+90\displaystyle {f{{\left({x}\right)}}}=-{16}{t}^{{2}}+{8.6}{t}+{90}, where t\displaystyle {t} is measured in seconds.
How long will it take the cell phone to hit the ground? Round your answers to three decimal places.

seconds