What does sound travel the fastest throught wood, water, vacuum or air

How much work is done lifting a 9.10 kg box straight up onto a shelf that is 1.80 m high?

With i really need the correct answer!

Which explanation describes the forces involved for a person to walk down the sidewalk? a. the person's feet push backward on the sidewalk; the sidewalk pushes backward on the person. b. the person's feet push forward on the sidewalk; the sidewalk does not push on the person. c. the person's feet push backward on the sidewalk; the sidewalk pushes forward on the person. d. the person's feet push forward on the sidewalk; the sidewalk pushes forward on the person.