As shown in the figure, a plane rectangular coordinate system is established.

Let AB and y axis intersect at h,

AB = 36

∴AH=BH=36/2= 18

According to the question:

OH=7 CH=9

∴OC=9+7= 16

Let the analytical formula of parabola be:

y=ax^2+k

Vertex C(0, 16)

∴ parabola y = ax 2+16

Substitution point (18,7)

∴7= 18× 18a+ 16

∴7=324a+ 16

∴324a=-9

∴a=-9/324=- 1/36

∴ parabola: y =- 1/36x 2+ 16

When y=0,-1/36x2+ 16 = 0.

∴- 1/36x^2=- 16

∴x^2= 16×36=576

∴x= 24

∴E(24,0),D(-24,0)

∴OE=OD=24

∴DE=OD+OE=24+24=48

As this is a practical problem, ∴DE=48m.