Answer-
The length of line segment WU is 4 cm.
Option 1. 4 cm is correct.
Solution-
As given that, RSTU is an parallelogram.
RT and SU are its two diagonals. They intersect each other at point W.
Properties of parallelogram is that they bisect each other.
i.e SW = WU and RW = WT
As given that, SW = 4 cm.
So, WU = SW = 4 cm
Therefore, the length of line segment WU is 4 cm.