∠B=∠D
So triangle ABE is congruent with triangle AFD.
BE=DF
Then CE=CF
CEF= Treaty on Conventional Armed Forces in Europe
∠CEF+∠CFE+∠C= 180
∠B+∠C= 180
So ∠B=∠CEF+∠CFE=2∠CEF.
∠B=∠AEB
∠AEB=2∠CEF
∠AEB+∠AEF+∠CEF= 180
2∠CEF+60 +∠CEF= 180
∠CEF=40
∠B=80