Well, after a couple of hours of work, I figured out how to get K explicit in the first equation. I came up with the following:
K = (-R[1-e^([W*pi]/[D*ln([1+R]/[1-R])])])/(1+3^[(W*pi)/(D*ln[(1+R)/(1-R)])])
It should be fairly easy to subsititute the second equation in for R, and then substitute that entire thing into the third equation.
Sorry for the sloppy text, LaTeX really doesn't like me. I'll attach a picture to make it easier to read.
What value of K do you get when W= 5, D=5 & B=10? Does it match what I got via numerical methods?