A Beer-Lambert Analysis Showed the Extinction Coefficient for Compound B $\mu$

A Beer-Lambert analysis showed the extinction coefficient for compound B in water to be 345 m² mol⁻¹ at 450 nm. A different solution of compound B is analysed by UV/visible spectroscopy and the absorbance at 450 nm is recorded as 0.28 in a 1.00 cm cell. What is the concentration of this solution?

A) 8.1 × 10⁻⁴ mol dm^-3
B) 1.2 mmol dm^-3
C) 12 mol dm^-3
D) 8.1 $\mu$ mol dm^-3