First of all you have to make them equal to each other. What I mean is the following
3x+20=2x+40
Then you should just solve for x
Similar polygons only differ by a scaling factor. In other words, two polygons are similar if one is the scaled version of the other.
In particular, this implies that the angles are preserved, and the correspondent sides are in proportion.
These two polygons are both rectangles, so the angles are preserved. We must check the sides, and we have to check if the smaller sides are in the same proportion as the bigger sides.
So, the two rectangles are similar if the following is true.

In any proportion, the product of the inner terms must be the same as the product of the outer terms:

This is clearly false, and thus the two rectangles are not similar.
Step-by-step explanation:
3(-8m-1) + 5(m+8) (remove the parentheses)
-24m - 3 + 5m + 40 (collect like terms and calculate)
-19m + 37
Answer:
Line M would also have a slope of 2/3.
Step-by-step explanation:
When two line are parallel that means that they will never intersect.
In order for two lines to avoid intersection they would have to be at the same slope.
Since lines K and line M are parallel to each other they have to have the same slope.
Answer:
I'm not sure what your asking, but, no, all rectangles are parallelograms.
I found this over the internet, and I hope it helps you understand why a rectangle is always a parallelogram, but a parallelogram is not always a rectangle:
It is true that every rectangle is a parallelogram, but it is not true that every parallelogram is not a rectangle. For instance, take a square. It's a parallelogram — it is a quadrilateral with two pairs of parallel faces. But it is also a rectangle — it is a quadrilateral with four right angles.