Answer from cs61c-cb (Minh Uyen Nguyen 16765774) for Question 1
The fact is that with virtual memory, the CPU produces a virtual address, which is translated by a combination of hardware and sofware to a physical address, which in turn can be used to access memory.
Therefore, the difference between VA and PA is that VA is the address produced by CPU and cannot be used to access memory without being translated to PA.

Physical Page Number= PageTable[Virtual Page Number]

Physical Page Address = the leftmost bits with the virtual address rightmost offset bits being cut off.