141. Solving a chemistry problem

To build a calibration graph for the determination of tin in bronze, the following results were obtained:
W (Sn),% 6.23 8.02 9.34 11.63
∆S 0.690 0.772 0.831 0.910
Photometry of the spectrum taken through a three-stage attenuator showed that for two stages of the Sn line ∆Sstop = 1.055. By photometry of the spectrum of bronze samples photographed on another plate, ∆S step was obtained for two steps of the same Sn line (see above), and for the analytically Sn-Cu pair in the spectrum of the sample on the same plate Sx. Determine the mass fraction of tin in the samples:
Sample 1
∆S t 0.930
∆Sx 0.635