So since m is on both sides of the equal sign, they cancel each other out. Then multiply both sides by 2, so you get 2gh = v². Then (I'm assuming) g = acceleration due to gravity = 9.80 m/s². If you multiply it by the two, you get 19.6 m/s². I'm assuming h is the height, in meters. If you have the number for h, plug it in now and multiply that. You'll get some number x that has a value of m²/s². Since you're looking for v, and right now you only have v², take the square root of both sides of your equation and that'll give you the answer. If you don't have a value for h, though, just write your answer like √(2gh) = v or whatever format like that your teacher usually wants, and you should be good. I don't know how far the teacher wants you to simplify or solve this, but hopefully this gives you what you need! :)
The student does zero work on the backpack because the upward force applied by the student is acting <em>perpendicular</em> to the backpack's displacement parallel to the ground.
Langerhans cells exist on the surface of the skin. They help to protect you by keeping dangerous microbes from entering your body. Langerhans cells do this in two very different ways: by protecting your skin from infection and also by stimulating allergic reactions.