Ms. Wolfram should ask her husband Stephen, who's an incredible mathematician and computer scientist who's given the world a great gift in the website Wolfram Alpha which can answer all your math questions and more.
Anyway the volume of the bin is length times width times height,
V = 4 × 18 × 9 = 648 cubic inches
So the volume of brown is 20 % of that
B = 20% of V = .2 × 648 = 129.6 cubic inches
The volume of green is 30%,
G = 30% of V = .3 × 648 = 194.4 cubic inches
Answer: Green 194.4 cubic inches, Brown 129.6 cubic inches