Question 729962
You have your equation for height as a function of time, {{{h(t)=-16t^2+240t}}}. You are asked exactly,  find t for {{{ h(t)=0}}}.  This question on that equation is clear.  {{{-16t^2+240=0}}}, so find t.  What kind of equation is that?  Do you remember a general method to find a solution?