I am trying to use the Given - Find Solve Block to determine the embedded length for a circular pile foundation given in an ASCE article, "Resistance to Overturning of Single, Short Piles", E. Czerniak, Journal of the Structural Division, Paper 1188. The attached worksheet contains an equation for the required length for a given pile diameter with a set of lateral and vertical loads. Any comments on why the error message resulting from the Find(L) statement would be appreciated.
You have a unit mismatch in your formula. L^3 is volume, but the other two summands are of dimension length.
Your units for R are wrong. You have lbf/ft, should be pressure per ft (psi/ft):