What three machines or devices depend of gravity to work?

Determine the amount of work done when a crane lifts a 100-n block form 2m above the ground to 6m above the ground

Part a constants huck finn walks at a speed of 0.60 m/s across his raft (that is, he walks perpendicular to the raft's motion what is huck's velocity (speed and direction) relative to the river bank? express your answer to three significant figures and include the appropriate units. relative to the shore)

Could someone me find the answer to this problem.