Formula: Horizontal throw Throw duration Initial height
$$t_{\text d} ~=~ \sqrt{ \frac{2\, y_0}{ g } }$$
$$t_{\text d} ~=~ \sqrt{ \frac{2\, y_0}{ g } }$$
$$y_0 ~=~ \frac{ g }{ 2 } \, {t_{\text d}}^2$$
$$g ~=~ \frac{ 2 \, y_0 }{ {t_{\text d}}^2 }$$
Throw duration
$$ t_{\text d} $$ Unit $$ \mathrm{s} $$
Throw duration (in general: flight duration) is the time after which the thrown/shot body lands on the ground.
Initial height
$$ y_0 $$ Unit $$ \mathrm{m} $$
Initial height is the distance from the throw/shot position to the ground.
Gravitational acceleration
$$ g $$ Unit $$ \frac{\mathrm{m}}{\mathrm{s}^2} $$
Gravitational acceleration is a constant acceleration experienced by all freely falling bodies near the ground. It has the value:
$$ g ~=~ 9.8 \, \frac{\mathrm m}{\mathrm{s}^2} $$