Question 1154978
{{{h=-16t^2-16t+60}}}, where {{{h}}} is the height in {{{ft}}} and {{{t}}} is the time in seconds

 the rock will hit the surface when {{{h=0}}}

to find how long it will took the rock will hit the surface,plug in {{{h=0}}} and solve for {{{t}}}

{{{0=-16t^2-16t+60}}}........factor out {{{-4}}}

{{{0=-4(4t^2+4t-15)}}}...write {{{4t}}} as {{{10t-6t}}}

{{{0=-4(4t^2+10t-6t-15)}}}

{{{0=-4((4t^2+10t)-(6t+15))}}}

{{{0=-4(2t(2t+5)-3(2t+5))}}}

{{{0=-4(2t -3)(2t + 5)}}}

solutions:
 
if {{{0=(2t -3)}}}=>{{{2t=3}}}=>{{{t=3/2}}}=>{{{t=1.5}}}

if {{{0= (2t + 5)}}}=>{{{2t=-5}}}=>{{{t=-5/2}}}=> disregard negative solution


so, it took {{{1.5}}} seconds the rock to hit the surface