∫∠FEC = 90

∴∠AEF+∠ced = 90∠AFE+∠DCE =∠AEF+∠ced = 90。

AE=AF, that is, ∠AFE=∠AEF.

∴∠DCE=∠CED, then CD=DE.

Ae: de = 3: 5

∴AF:AE:DE:CD=3:3:5:5

Let AF = AE = 3xde = CD = 5x (x > 0).

Then AD=AE+DE=8x BF=AB-AF=CD-AF=2x.

Lian DF

Then s1:s △ ADF = AE: ad = 3x: 8x = 3: 8.

S2:S△ADF=BF:AF=2x:3x=2:3

While S2+S△ADF= 1/2□ABCD=20, that is, 2/3S△ADF+S△ADF=20, the solution is S△ADF= 12.

∴s 1+s2=3/8s△adf+2/3s△adf=25/24s△adf=25/2

You must use hand-to-hand combat to do the task.