Solve the all parts of following problem:
Problem: While standing at the edge of the roof of a building, you throw a stone upward with an initial speed of 6.41 m/s. The stone subsequently falls to the ground, which is 11.9 m below the point where the stone leaves your hand.
Part A: At what speed does the stone impact the ground?
Part B: How much time is the stone in the air? Ignore air resistance and take g = 9.81 m/s2.
I know the correct answer for above problem but explain how to get this answer! Thank you.