How would you get the concentration(ppm) of a sample from absorbance?

Question

Absorbance of standard = 2.55
Absorbance of sample = 2.31
Wavelength of machine 345nm
slit lenght = 1cm
time = 2s
The metal being tested is Copper and the concentration of the standard is 8ppm.

Answer 1

Absorbance std = k*concn std
2.55 = k*8
Solve for k.

Absorbance sample = k*concn sample
2.31 = k from above*concn sample
Solve for c sample.