A student measures k for a certain blue due to be 19.4 m^-1 at 560 nm. What is the molarity of the dye in a solution with an absorbance of .118 at this wavelength ?

A = abc and we will call a*b = k, then

A = kc
You know A = 0.118
You know k is 19.4
Solve for c in mols/L