We can use the formula y2-y1/x2-x1 to find slope given two points. Therefore, we have -1-8/-2-1, getting us -9/-3, or just 3. Hope this helps!
Answer:
37.5 
Step-by-step explanation:
As the area of each of the side of the cube are the same we can multiply the area of one side by 6.
The area of one side is

-x + y = 4
2x + y = 1
-3x = 3
-3 -3
x = -1
2x + y = 1
2(-1) + y = 1
-2 + y = 1
+ 2 + 2
y = 3
(x, y) = (-1,3)