I like doing this in the following manner....construct a square with a side = 4 [ any side length would work ]
Let A = (0,0) B = (0,4) C = (4,4) and D = (4,0) E = (2,4) F = (4,2) M = (0, 2)
Here's a pic :

Triangles BCF and DAM are congruent right triangles
And the slope of BF = [ 4-2] / [ 0 - 4 ]= 2/-4 = -1/2
And the slope of EA = [ 4-0] / [2-0] = 4/2 = 2
So....these segements have reciprocal slopes so they are perpendicular
This means that triangles BCF and BGE are similar by AA congruency
BC = 4 CF = 2 BE = 2 BF = √ [ BF^2 + CF^2] = √ [4^2 + 2^2] = √20 = 2√5
So.....by similar triangles...... BG / BE = BC/ BF → BG/ 2 = 4/ [ 2√5 ] → BG = 4/√5
And GE = √[BE^2 - BG^2] = √[2^2 - (16/5] = √ 4 - (16/5] = √ [ 20 - 16] / √5 = 2/√5
And the area of triangle BCF = (1/2) BC * CF = 4
And since BG / BC = ( 4 / [ √5] ) / 4 = 1/ √5.....the area of triangle BGE = 4 (1/√5)^2 = 4/5
Likewise triangles MAD and MNA are similar and we can show that triangles BGE and ANM are congruent
So....BG/MN = BG / GE = [4/√5 ] / [2 /√5] = 2
And FG = BF - BG = 2√5 - 4/√5 = [10 √5 - 4√5] / 5 = 6√5/5 = 6/√5
So....FG/ MN = 6/√5 / [ 2/√5] = 6/2 = 3
And DN = DM - MN = BF - GE = 2√5 - 2/√5 = [ 10√5 - 2√5] / 5 = 8√5/5 = 8/√5
So DN / MN = [8/√5]/ [2/√5] = 8 /2 = 4
Area of BMDF = Area of the square less areas of BCF and DAM = 4^2 - 2 [4] = 16 - 8 = 8
Area of GBMN = area of BEA - areas of BGE and ANM = (1/2)BE * BA - 2(4/5) =
(1/2)(2)(4) - 8/5 =
4- 8/5 =
[20 - 8] / 5 =
12/5
So the area of GFDN = area of BMDF - area of GBMN = 8 - 12/5 = [40 - 12]/5 = 28/5
So GFDN / GBMN = [ 28/5] / [ 12/5] = 28/12 = 7 / 3
