It’s the third graph down!!
since a square must be the same length on all sides to be a correct square, you can legit just multiply the length of one side times four to get the area.
3.2 x 4 = 12.6
-(-4) = 4, so the opposite, if I understand what they mean, would be -4.
If it's a regular octahedron, then you can calculate it using the formula

where

is the length of the edge.
If it's not regular, you have to calculate the area of each side individually.
Answer:

Step-by-step explanation:
Given, y = 0.8
To find : value of x

plug the value of y

Multiply the numbers: 8 and 0.8

Move 6.4 to right hand side and change it's sign

Subtract 6.4 from 40

Divide both sides by 4

Calculate

Hope I helped!
Best regards ! :D