How do I find the instantaneous rate of change when

f(x)=3x-4; x=2

I know that the limit as h->0 is

[f(x+h) - f(x)]/h

but I'm not sure how to plug in the 3x-4. I was able to find the limit when f(x) = x^2 just by [(x+h)^2 - x^2]/h, but I can't seem to find the correct way to get 3x-4 into the equation (I keep ending up w/a 0 in the denominator no matter what I try).