Here is some instructions on how to do PS. 1. For the concepts in Question 1, you need to read textbook to find out and understand what they are. 2. The textbook will also teach you have to derive the market demand curve from the individual demand curves. 3. See the 2nd attachment for a short example on how to do maximization, which might of help for doing the 3rd question. The key to this question is to set up your objective function, namely, what you want to maximize. Then you can consult my example on how to calculate the maximized value.
Here is the video lecture link:
Here is the textbook that I mentioned about:
Microeconomics and Behavior by Robert Frank, 2015, 9th Ed., McGraw-Hill
Let me know if you have any further questions.