What does gatsby's library of uncut books symbolize? and why

Uncut books usually indicate that no one has used them, implying that Gatsby merely had the books to display his wealth. Although this is ostentatious, Gatsby had a reason to impress (I don't know if you finished the novel, so I don't want to continue with spoilers.)

substitute y = 2x - 4 to x + 2y = 12:

x + 2(2x - 4) = 12     use distributive property

x + (2)(2x) + () = 12

x + 4x - 8 = 12     add 8 to both sides

5x = 20     divide both sides by 5

x = 4

put the value of x to the first equation:

y = 2(4) - 4

y = 8 - 4

y = 4