a) Bill kicks a rock off the top of his apartment building. It strikes a window across the street 16 m away. The acceleration of gravity is 9.8 m/s^2.If the window is 17 m below the position where Bill contacted the rock, how long was it in the air? Answer in units of s.
b) How fast was it moving when it left Bill’s foot? Answer in units of m/s.

I kindly ask for some help, mainly in part b, thanks!