Beer-Lambert Law applies most accurately at low concentrations, so I'd use the 0.00001 mol / L absorbances as the basis for calculations.
This means that for Cu(II) the "after treatment" concentration is 0.040 / 0.140 x 0.00001 mol / L = 0.00000286 mol/L
and for Pb(II) the "after treatment"...
The responses and questions above are excellent. I'd like to add a perspective that I have found to be helpful with my own HSC Physics students.
If you are asked a question about energy quantisation, use the visible emission spectra of the hydrogen atom as your example (or absorption...