For A, 5x4x3=60
for B 5x3x2=30
for C 5x4x1=20
for D 5x4x2=40
hence, A has a volume of 60cubic units!
By finding the volume of the shape
N4=c
n times 4, n being a number of notebooks, would equal c, or the overall cost.
You can have a maximum of 3 groups. This is due to the fact that you only have 3 sopranos to equally divide between groups. Over 3 you would have a group lacking a soprano so 3 is the greatest you can make it.