We are asked to find the value of b that makes quadrilateral RSTU a parallelogram.
We know from the properties of a parallelogram that the opposite angles are always equal.
[tex]\begin{gathered} \angle S=\angle U \\ \angle T=\angle R \end{gathered}[/tex]
Let us equate the angles and solve the equation for b.
[tex]\begin{gathered} \angle S=\angle U \\ 11b-6=12b-18 \\ 11b-12b=-18+6 \\ -b=-12 \\ b=12 \end{gathered}[/tex]
Similarly,
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