Question 286760
<pre><font size = 4 color = "indigo"><b>
I will assume thie rectangle is like this:

{{{drawing(400,300,-1,4,-1,4,
locate(0,2.3,R), locate(3,2.3,S), locate(1.4,.9,Z), locate(0,0,W),
locate(3,0,T),
rectangle(0,0,3,2), red(line(1.5,1,0,2)), triangle(1.5,1,3,0,3,0),
green(line(0,0,3,2))  )}}}

The red line RZ is 2x+5.  

The diagonals of a parallelogram bisect each other.

The red line RZ, which is 2x+5 is one-half of the diagonal RT.

The diagonals of a rectangle are equal.  So

    2(RZ) = RT = SW

    2(RZ) = SW

2(2x + 5) = 5x - 20
 
  4x + 10 = 5x - 20

       30 = x

Edwin</pre>