A quadratic function problem

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?*