Solve the all parts of given problem:
Problem: A rock is thrown vertically upward with a speed of 18.0m/s from the roof of a building that is 40.0mabove the ground. Assume free fall.
Part A: In how many seconds after being thrown does the rock strike the ground?
Part B: What is the speed of the rock just before it strikes the ground?
I am not able to get the correct solution please help me.