DE is the perpendicular bisector of AC.
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Step-by-step explanation:
AB=BC
8x+6=6x+18
2x=12
x=6
so
AB= 48+6=54cm
BC=36+18=54cm
AD=CD
8y+20=12y-8
-4y=-28
y=7
so
AD= 84-8=76cm
CD=56+20=76cm
AE=2x+4y
AE=2×6+4×7
AE=40cm
AC=2×40=80cm