You do have a number, it’s just not written down! It’s that a full circle is 360 degrees
Let x + y = d and w + z = e for easier writing
We know d + e = 360 degrees (a full circle)
d = e, so 2d = 360, so d = 180 degrees
The angle AOB = d, and d = 180 degrees, so AB is a straight line
The actual maths is really easy, the bit that I assume is tripping you up is the realisation that you have more information than the words of the question
You do have a number, it’s just not written down! It’s that a full circle is 360 degrees
The actual maths is really easy, the bit that I assume is tripping you up is the realisation that you have more information than the words of the question