Given that both secants are equal, we can deduct that arcs AB and DC are equal.
We know that the whole circumference is 360°.
[tex]\begin{gathered} 85+13x-21+31+13x-21=360 \\ 26x=360-74 \\ 26x=286 \\ x=\frac{286}{26} \\ x=11 \end{gathered}[/tex]Hence, x is equal to 11.