In one of the cuvettes, you mix 0.90 ml of 3.0 mm proflavine, 0.40 ml of 26.4 µm DNA, and 0.70 ml buffer. What is the concentration, in µm, of the DNA in this cuvette?
a. 22.0 µm
b. 26.4 µm
c. 30.0 µm
d. 33.6 µm