Question 576648
Start with:
{{{h(t) = -9.8t^2-10t+290}}} 
When the stone hits the ground, h(t) = 0, so...
{{{0 = -9.8t^2-10t+290}}} Solve this quadratic equation using the quadratic formula: {{{t = (-b+-sqrt(b^2-4ac))/2a}}} where: a = -09.8, b = -10, and c = 290.
{{{t = (-(-10)+-sqrt((-b)^2-4(-9.8)(290)))/2(-9.8)}}}
{{{t = (10+-sqrt(100-(-11368)))/(-19.6)}}}
{{{t = (10+-sqrt(12368))/(-19.6)}}} Evaluate.
{{{t = 4.95}}}secs. or {{{t = -5.974}}}secs. Discard the negative solution as the time is a positive quantity.
The stone will hit the ground after 4.95 seconds.