0.1 mL of a protein solution of concentration of 6 mg/mL was diluted to a total volume of 4.0 mL with water (i.e. 0.1 mL of the solution was added to 3.9 mL of water). 3 mL of this solution was then mixed with 27 mL of water.
A) 0.15 mg/mL
B) 0.06 mg/mL
C) 0.5 mg/mL
D) 0.9 mg/mL