The table represents a linear function. what is the slope of the function?

Using the equation of a straight line, which states:

                                    y = mx + b
where,
m represents the slope
y represents the y-intercept.

Therefore,
To find the slope,
we would select any of the two coordinate points and find the slope.
To calculate the slope of a line you need only two points from the table;
                         
                                       (x₁, y₁) and (x₂, y₂)

x₁ = - 4
x₂ = - 2
And,
y₁ = -2
y₂ = - 10

m = (y₁ - y₂) ÷ (x₁ - x₂)

Substituting the values,

m = (-2 + 10) ÷ (-4 + 2)

m = 8 ÷ (-2)

m = -4 is the required slope.

Yes, two vertical lines can be complementary