12. Solving a chemistry problem

2. During photometric titration on a photocolorimeter of 10 ml of a KMnO4 solution with a NaNO2 solution, the titer of which is 0.0015 g/ml, the following data were obtained:
VNaNO2, ml 0 0.5 1.0 1.25 1.5 1.75 2.0
Galvanometer readings 50 59.0 66.5 75.0 77.5 77.0 78.0
Determine the concentration of the KMnO4 solution (g/l) if the deviation for the background was 80 divisions of the photocolorimeter scale.