Calculate the concentration of a solution of peptide GRAYISH, in mM if the absorbance at 280 nm for the solution is 0.5 absorbance units, and a 0.3-cm cuvette is used. For the extinction coefficient, take into account that ϵ₂₈₀(Trp) = 5690 M^-1 cm^-1 and ϵ₂₈₀(Tyr) = 1280 M^-1 cm^-1.