A ball is thrown upward in the air, and its height above the ground after $\displaystyle {t}$ seconds is

$\displaystyle {H}{\left({t}\right)}={69}\cdot{t}-{16}{t}^{{2}}$ feet.

Find the time $\displaystyle {t}$ when the ball will be traveling upward at $\displaystyle {34.5}$ feet per second.

Give your answer as a decimal approximation with at least 3 decimal places.

$\displaystyle {t}=$ Preview Question 6   seconds