∠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