The perimeter would be (24x - 40)/(x^2 - 4x).
In order to find this, first double the length and width as you would to find any perimeter.
7/(x - 4) * 2 = 14/(x - 4)
5/x * 2 = 10/x
Now to add those together, we need to give them common denominators. In order to do that with the first one, we need to multiply by x/x
14/(x - 14) * x/x = 14x/(x^2 - 14x)
Then we can do the same with the second part by multiplying by (x - 4)/(x - 4)
10/x * (x - 4)/(x - 4) = (10x - 40)/(x^2 - 14x)
Now we can add the two together
14x/(x^2 - 14x) + (10x - 40)/(x^2 - 14x) = (24x - 40)/(x^2 - 14x)