From the information provided, we can deduce the following;
Note that
[tex]\begin{gathered} \angle ABC=\angle DEC \\ \text{Both angles are marked in red as shown in the attachment} \end{gathered}[/tex]Also, note that
[tex]\begin{gathered} \angle GFE=\angle DCE \\ \text{Both angles are marked in blue} \end{gathered}[/tex][tex]\angle ACB=\angle DCE\text{ (vertically opposite angles are equal)}[/tex]If angle ACB equals angle DCE, and DCE equals GFE, then it means;
[tex]\angle ACB=\angle GFE[/tex]Similarly;
[tex]\angle GEF=\angle DEC\text{ (Vertically opposite angles are equal)}[/tex]In the same manner as the other angle as explained above,
[tex]\angle GEF=\angle ABC[/tex]