Geometry: Common Core (15th Edition)

$RE = 3.5$
In a parallelogram, diagonals bisect one another. If diagonal $\overline{AE}$ is bisected by diagonal $\overline{CP}$, then the bisected segments $\overline{AR}$ and $\overline{RE}$ are equal to one another. So if $AR = 3.5$, then $RE$ also equals $3.5$.