Question 701779
They are asking when {{{ h = 0 }}} for the 2nd time.
{{{ h = 128x - 16x^2 }}}
{{{ 0 = -16x^2 + 128x }}}
{{{ 0 = x*( -16x + 128 ) }}}
{{{ -16x + 128 = 0 }}}
{{{ 16x = 128 }}}
{{{ x = 8 }}}
The ball hits the ground in 8 seconds