6. simplify the following expression by combining (adding together what is alike) like terms:
8n + 5 - n + 13
*
9n + 18
13n + 12
25n
7n + 18

7. what is the domain (the first element or number, from each pair) of this relation:
{ (4,1), (5,2), (6,-1), (8,5) }
*
{4, 5, 6, 8}
{4, 5, 6}
{-1, 2, -1, 5}
{4, -1, 5, 2}

8. on a number line, which are greater: *

absolute numbers
negative numbers
positive numbers
no numbers