Solve the given parts of following problem:
Problem: You throw a 20-N rock vertically into the air from ground level. You observe that when it is a height 15.2m above the ground, it is traveling at a speed of 24.6m/s upward.
Part A: Use the work-energy theorem to find its speed just as it left the ground.
Part B: Use the work-energy theorem to find its maximum height.
I need help to find its speed just as it left the ground.