47. Solving a chemistry problem

5. To determine potassium in a mineral fertilizer, a sample weighing 1.000 g was dissolved in water when heated, transferred to a volumetric flask with a capacity of 250.0 ml and filtered. The filtrate was diluted with water 50 times. During photometry in a flame, the current strength was 18.5 μA. Photometry under similar conditions of standard potassium chloride solutions yielded the following data:
C(C), mg/l 5.00 10.00 15.00
I, µA 8.0 15.0 24.0
Find the mass fraction of potassium chloride in the fertilizer.