There are at least three ways to get answers in Mathcad:
> Numerical processor using the Given/Find or Given/Minerr, or Root Finder
> Symbolic processor can solve algebraic problems symbolically, on occasion
> Symbolic processor can also find roots numerically
TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!
Also attached is the sheet itself. I wasn't sure that first set of brackets are actually necessary, so I included them. I upped the precision on the symbolic solver's solution so that the answers from the symbolic and numerical solvers came out the same. Note that the Given/Find requires a guess value for D, which was already calculated by the symbolic solver, but typically, anything close to the actual answer will work, and sometimes, even a guess that's far away will work as well.