A waterfall has a height of 1400 feet. A pebble is thrown upward from the top of the falls with an initial velocity of 12 feet per second. The​ height, h, of the pebble after t seconds is given by the equation h equals negative 16 t squared plus 12 t plus 1400
h=−16t2+12t+1400. How long after the pebble is thrown will it hit the​ ground?