If you already know the value of n, all that's necessary to do for these problems to simply plug in it as shown:
1.) [tex]5n + 3n --> 5(3) + 3(3)[/tex]
---> [tex]15 + 9 = 24[/tex]
2.) [tex]9(x - 7) - y[/tex] --> [tex]9(11 - 7) - 19[/tex]
---> [tex]9(4) - 19[/tex]
----> [tex]36 - 19 = 17[/tex]
