Can someone please solve or tell me how i would do this question. I'm finding it really difficult.

A projectile is launched from the top of a building. The height (h meters) of the projectile above the ground is given by the equation h=15 + 20t - 2t^2 where t is the time of flight in seconds.

(a) sketch the graph to represent the flight

(b) What is the greatest height reached?

(c) What is the height of the building?

(d) After what time did the projectile strike the ground?