[tex]557 = 9(55 + x) + 8[/tex]
[tex]557 =495 + 9x + 8[/tex]
[tex]9x = 557 - 495 - 8[/tex]
[tex]9x = 62 - 8[/tex]
[tex]9x = 54[/tex]
[tex]x = 54 \div 9[/tex]
[tex]x = 6[/tex]
[tex](607 - x) \div 31 = 19[/tex]
[tex]607 - x = 19 \times 31[/tex]
[tex]607 - x = 589[/tex]
[tex] - x = 589 - 607[/tex]
[tex] - x = - 18 \: | \times ( - 1)[/tex]
[tex]x = 18[/tex]