A rational function has a slant asymptote if and only if it meets
both these conditions:

1. The degree of the the numerator is 1 more than the degree of
the denominator.

2. When the denominator is divided into the numerator, a non-zero
remainder is obtained.  

3. If so then  is the equation of
the slant asymptote.

--------------------------------------

?

The degree of the numerator is 2 (largest power of x is 2)
The degree of the denominator is 1 (largest power of x is 1)

Therefore it meets the first condition. Let's see if it meets
the second condition:

            x - 2
x - 4)x² - 6x + 8
      x² - 4x
          -2x + 8
          -2x + 8
                0

No, it leaves a zero remainder.  So R(x) does not have a
slant asymptote.

The correct choice is d
Edwin