141. Solving a chemistry problem

A glass sample weighing 0.1000 g was dissolved in a mixture of H2So4 and HF, the solution was evaporated, the residue was moistened with HCl and transferred to a 250 ml volumetric flask. The resulting solution was photometric in flame in the same way as standard solutions prepared from NaCl. Photometry data are given in the table (Irel is the relative radiation intensity):
Parameter Standard solution Sample
СNa, mg / l 10.0 20.0 30.0? ? ?
Irel 16.0 31.5 47.5 24.0 35.0 42.5