Answer:
Equation: 4x - 6 = 6 x = 3
Explanation:
A rectangle is a parallelogram, which means that opposite sides are parallel. This means that both of the short sides equal 12. 12 plus 12 is 24, so substract 24 from 36 to get 12. This means that the sum of the long sides are 12; half of 12 is 6 so that is the length of one of the sides. This means that you can set the equation 4x - 6 equal to 6. Add 6 to both sides to get 4x = 12, then divide both sides by 4 to get x = 3. I think your equation should be 4x - 6 = 6, and x equals 3.
Sorry if I'm wrong, if I'm right then that picture of the rectangle is really misleading.