30. Solving a chemistry problem

131. To determine the wavelength of a given line in the spectrum of the analyzed sample, two lines in the spectrum of iron with wavelengths λ1 and λ2 were selected. The readings on the measuring microscope scale for these lines were equal to b1 and b2, respectively (see table). Determine the wavelength of a given line if the scale reading for it is equal to bx.
option Wavelengths of selected iron lines, nm Readings on the microscope scale, mm
λ1 λ2 b1 b2 bx
131 373.718 374.560 5.09 6.19 5.68