to be a parallelogram its front sides must be equal to each other
so, we equalize the length of two sides that are face to face
[tex]\begin{gathered} 5w-25=w+15 \\ \\ \end{gathered}[/tex]and solve for w
[tex]\begin{gathered} 5w-w=15+25 \\ 4w=40 \\ w=\frac{40}{4} \\ \\ w=10 \end{gathered}[/tex]the value of w must be 10