calculus word problem, help plz?

AP Calculus help anyone?

1.Use the position function s(t) = -16(t)^2 + vo(t) + so for free- falling objects.

Question - A ball is thrown straight down from the top of a 220-foot building with an initial velocity of -22 feet per second. What is its velocity after 3 seconds? What is its velocity after falling 108 feet?

2. Use the position function s(t) = -4.9(t)^2 + vo(t) + so for free falling objects.

Question - To estimate the height of a building, a stone is dropped from the top of the building into a pool of water at ground level. How high is the building if the splash is seen 6.8 seconds after the stone is dropped?

I'm in calculus AP, and I'm really uncomfortable with velocity problems. Help please?