Equation 1 ==> y - x = -13
Equation 2 ==> -4x + 3y = -51
3(y - x) = 3(-13)
Equation 3 ==> 3y - 3x = -39
Equation 2 - 3
= (3y - 3y) + ( -4x - (-3x) ) = -51 - (-39)
-x = -12
x = 12
Substitude x into equation 1
y - 12 = -13
y = -1
I think the answer would be 36:16 because if you do the area of the first figure (6x6) it equals 36 and the second figure (4x4) it equals 16
There follows the formula for "z-score:"
raw score - mean
z = ------------------------------
standard dev
9.1 - 8
Here, the z-score is z = ------------- = 0.344
3.2
This is a problem where you should make an equation.
Let's say x is the first week. It would mean
First Week : x
Second Week : x + 5
Third Week : 2(x+5)
You need to add these up to make your equation. Your equation will look something like this :

Now you simplify.



That means they sold 104 Boxes in the First Week.
So they sold 109 Boxes the Second Week.
109 x 2 = 218
And they sold 218 Boxes the Third Week.
I hope I was useful!