To solve this problem, we need to know the relationship between the absorbance at a particular wavelength and the concentration of the given dye. The dye concentration is measured (typically) in common concentration units, such as M.
In other words, the absorbance values for different concentrations of the dye are needed. This data will be then be plotted, with absorbance values on the y-axis and the concentration values on the x-axis. The relationship between the absorbance and the dye concentration can then be found out by fitting the equation of the line (y = mx + c) to the given data.
Using this relationship, the concentration can be found at any other value of absorbance.
For example, say, the relationship between absorbance (y) (measured at 590 nm) and dye concentration (x) is given as:
y = 71620x - 0.0247
then, we can substitute y = 0.63 to obtain x = 9.1 x 10^-6 M.
So for your case, kindly find the relationship between the absorbance and dye concentration and substitute the value of given absorbance (0.63) and obtain the required dye concentration.
Hope this helps.