For the given question , we have to use the following formula
[tex] x = \frac{Far \ arc - nearer \ arc}{2} [/tex]
And the measurement of two arcs are 100 and 20 respectively. So on plugging it in the formula, we will get
[tex] x = \frac{100-20}{2} = 40 \degree [/tex]
So the value of x is 40 .