What is the slope of this situation and what does it represent?

Think of two points on a straight line.  The first point is (0,8) representing 8 employees at time 0.  The second point is (6,26), representing 26 employees after six months have gone by.
                                               26-8
The slope of this line is m = = 18/6 = 3
                                                6-0

This indicates that 3 new employees are taken on on average each month.

This situation can be represented as 

E(x) = 8 + 3x, where x is the number of months that have passed, and E(x)
represents the number of employees at that point in time.