Hello,

I have a headache too

Look at this : Transversal line - Wikipedia, the free encyclopedia (i don't know the name of the angles in english)

Since AB and CE are parallel, angles BAC and ACE are equal.

We know that CE is the bisector of ACD. And ACD is 110°. So what's the value of angle BAC ?

Now, let's calculate angle OAC.

Use the theorem Inscribed angles with the center of the circle in their interior (Inscribed angle - Wikipedia, the free encyclopedia i really can't explain it in English, sorry...)

So you got angle OAC.

Then, you should know that there is a proportionality relation betwen this angle and the length of the arc :

OAC/360 = lengthOfTheArc/(perimeter of the circle)