Let's draw a diagram to represent the given problem.
If R is midpoint then PR and RQ are equal by definition of midpoint. So, we can express the following equation.
[tex]\begin{gathered} PR=RQ \\ 3x+6=5x-2 \end{gathered}[/tex]Then, we solve for x. First, we subtract 5x on each side.
[tex]\begin{gathered} 3x-5x+6=5x-5x-2 \\ -2x+6=-2 \end{gathered}[/tex]Now, we subtract 6 on each side.
[tex]\begin{gathered} -2x+6-6=-2-6 \\ -2x=-8 \end{gathered}[/tex]At last, we divide the equation by -2.
[tex]\begin{gathered} \frac{-2x}{-2}=\frac{-8}{-2} \\ x=4 \end{gathered}[/tex]We use this value to find PR and RQ.
[tex]PR=3x+6=3(4)+6=12+6=18=RQ[/tex]Then, we find PQ.
[tex]PQ=18+18=36[/tex]