Question 34797
What you are really trying to ascertain is...when will the height of the rocket be at zero feet - again?
You can find this by setting the equation h (height) = 0 and solving for the time (t).

{{{0 = 60t - 16t^2}}} Factor out a t.
{{{0 = t(60 - 16t)}}} Apply the zero products principle.
{{{t = 0}}} and/or {{{60 - 16t = 0}}}
When t = 0, the rocket has not yet stated its ascent.
{{{60 - 16t = 0}}} Add 16t to both sides.
{{{60 = 16t}}} Divide both sides by 16.
{{{t = 3.75}}}

The rocket returns to the ground after 3.75 seconds so it was in the air for 3.75 seconds.