It has to do with the number of dimensions you have in the figure. For example, in a square you have 2 dimensions, length and width. Since you have only two you use units^2. In a cube, you have 3 dimensions, length, width and height, which is where you get the units^3.
Combinations = n! / (n - r)! r!

In this case:
n = 4
r = 3
Combinations = 4! /(4-3)! 3! = 24/(1)(6) = 24/6 = 4
Answer:
4 arrangements
Answer:
I believe the answer is 3/7. Hope this helps!
Step-by-step explanation: