Solution:
The first thing to note is that the area of ABCD does not matter in this problem, so for the sake of convenience, introduce coordinates so that A=(0,0), B=(1,0), and C=(0,1).
Suppose A and B lie on the same side of ℓ2. Then, by symmetry, C and D lie on the same side of ℓ3. Now suppose BC intersects ℓ2 and ℓ3 at X and Y, respectively, and that DA intersects ℓ2 and ℓ3 at U and V, respectively. Note that XYVU is a parallelogram. Since BC=BX+XY+YC=BX+2XY>2XY, we have that XY is less than half the side length of the square, so the area of XYVU is at most half of the area of square ABCD. However, since 0.53>21, this can't happen. Similar reasoning applies if B and C lie on the same side of ℓ3. Therefore, points B and D lie between ℓ2 and ℓ3.
Let AB and AD intersect ℓ2 at points M and N, respectively. Let r=AM and s=AN. By symmetry, [AMN]=0.235, so rs=0.47. Additionally, in coordinates line ℓ2 is just rx+sy=1. Therefore line ℓ4 is given by rx+sy=3. Since C=(1,1) lies on this line, r1+s1=3.
The answer that we want is
1−42r+2s=1−2r+s
On the other hand, the condition r1+s1=3 rearranges to 3rs=r+s, so r+s=1.41. Thus the answer is 1−21.41=0.295=20059.