The UV absorption in proteins at 280 nm is largely due to tryptophan residues. The molar extinction coefficient of tryptophan is 5380 M-1cm-1. Exactly 0.25 g of a protein is dissolved in 200 milliliters of a neutral buffer. The molecular mass of the protein is 36,000 g mol-1. The absorbance of the solution at 280 nm in a 0.5 cm thick cuvette is 0.37. From this data, calculate the number of tryptophan residues that are found in one protein molecule.