First, you should factor both the numerator and the denominator. Since the numerator is the difference of two squares, that can be factored into (d-1)(d+1); for the denominator, you can factor out d to get d(d-1). From there, you can reduce both the numerator and denominator by (d-1) to get (d+1)/d. If you need to simplify it further, I believe you can simplify it to 1+(1/d).