The transmittance of a protein solution is measured at a wavelength of 280 nm in a cuvette with a path length of 1 cm.

The transmittance of a protein solution is measured at a wavelength of 280 nm in a cuvette with a path length of 1 cm. What is the concentration of the solution if 60% of the incident radiation is transmitted, and the molar extinction coefficient of the protein at 280 nm is ε280 = 74000 M-1cm-1 ?

Which formula should I use