There is a binding isotherm for an enzyme called a phosphatase and a lead compound known as JF99. There is a tryptophan near the binding site, and the fluorescence from this residue increase upon binding the compound. At the highest concentration of JF99 tested (1.2 μM), the fluorescence signal is 700 units. When the concentration is 30nM, the fluorescent signal is 400 units. The fluorescence signal is proportional to fraction of saturation or occupancy. Estimate the values of KD.