What is the main idea of percy jackson chapter 21

Percy tells Zeus the whole story and everything he knows. He gives Zeus the master bolt. Percy tells them his suspicions about Kronos, but Zeus firmly closes the subject. As he says goodbye to Percy, he tells him that he will spare his life this time, but Percy should never fly his skies again.

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