answer:Molar extinction coefficients are typically in M^-1* cm^-1 (aka 1/(M*cm)). If using a cuvette with a 1 cm path length, using the equation you give above the cm cancels and it gives you concentration in Molar, or Moles/Liter. If you multiply this by molecular weight (g/mol) moles cancel and you get g/L, which is equivalent to mg/mL. The units are because of the ****-Lambert law, which you rearranged in the above, A = ebc, where A is the absorbance (A280 in this case), e is the extinction coefficient, b is the path length, and c is the concentration. A has no units, thus the right side must cancel. If c is Molar and b is cm, e must be M^-1*cm^-1. Likewise, when it’s rearranged as above, there’s actually a b in the equation that’s dropped because it’s just 1 usually. So it’s really c = A/(eb). If A has no units, e = M^-1*cm^-1, and b = cm, cm cancels, and M^-1 is in the denominator and thus c is left to simply be M.