I'm not 100% sure what this all means because I'm in a different school but, I believe they have a side length of 4600.
P.S. If it doesn't work, I am so sorry
I will go about solving this using the elimination method.
First, convert the equations.
10x + y = -20
4x + y = -12
Second, find the easiest variable to get rid of and get rid of it! (In this case, y) We will subtract to get rid of y.
6x = -8
Third, you want to solve the equation.
6x = -8 (divide by 6)
x =

Fourth, solve for y by inserting the answer for x into one of the equations.
10(

) + y = -20

+ y = -20 (subtract

)
y =

The solution for this system of equations is (

,

).
When a set of objects are chosen from a larger set in which the order of the object doesn't matter, we call this combination. Otherwise if the order of selection would matter this would be called a permutation.
Probability is the likelihood of selecting a particular specified object in from a specified group of objects.
Therefore our answer is B.