The drawing seems to suggest that angles BFA, AFE and EFD span a straight angle, just like angles BFC and CFD
This means that you have
[tex]BFA+AFE+EFD=180 [/tex]
But we know that both BFA and EFD measure 70 degrees, so the equation becomes
[tex] [tex]70+AFE+70=180 \iff AFE + 140 = 180[/tex]
So, if you subtract 140 from both sides, you have
[tex] AFE = 180-140 = 40 [/tex]
