We know that:
The following property holds:
[tex]x=\frac{a+b}{2}[/tex]
Now, from the figure of the problem, using the previous property we say that:
[tex]\angle\text{AEC }=\frac{AC+BD}{2}[/tex]
But:
[tex]\begin{gathered} AC=110 \\ BD=40 \end{gathered}[/tex]
Finally:
[tex]\begin{gathered} \angle\text{AEC }=\frac{110+40}{2}=\frac{150}{2} \\ \therefore\angle\text{AEC }=75\degree \end{gathered}[/tex]
