I don't really know where to start, how could i go about awnsering this question? any help at all would be much appreicated..

"The height h(t) in feet of an object t seconds after it is propelled straight up from the ground with an initial velocity of 60 feet per second is modeled by the equation h(t)= -16t^2 +60t At what times will the object be at a height of 56 feet?"