Need help . Explain if you can . The options are
Additive property of length
All right angles are congruent
Definition of angle bisector
Definition of equilateral triangle
Definition of midpoint
Vertical angle theorem
The statement you're trying to justify is one that relates two line segments. (It says they're congruent.) This does not involve angles or triangles, and no addition of length is involved. The only reasonable choice on the list (and the correct one) is ...
Definition of midpoint
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A midpoint is a point that divides a line segment into two congruent parts. Since W is said to be the midpoint (given), it must divide UV such that UW ≅ VW, the statement we're trying to justify.
