Check the picture below.
you can do a search for the "inscribed quadrilateral conjecture", the proof is rather simple.
now, we know "x" cannot be a negative value, because that makes ∡C a negative angle, which is not feasible for this case.
we know ∡B = 7x - 10, and we also know what "x" is, thus
[tex]\bf \stackrel{\measuredangle B}{7x-10}\implies 7(12)-10\implies 84-10\implies 74 \\\\[-0.35em] ~\dotfill\\\\ \measuredangle B+\measuredangle D = 180\implies 74+d=180\implies d=106[/tex]
