Question 153687
You're looking for the time when {{{h=0}}} (when it has hit the ground)
{{{-16t^2 + s = 0}}}
{{{-16t^2 + 300 = 0}}}
{{{-16t^2 = -300}}}
{{{t^2 = 18.75}}} 
{{{t = 4.33}}}sec