We are given a triangle and told that line WY is a perpendicular bisector to side XZ. This line basically splits the triangle into two triangles: XYW and YZW.
Note that as both triangles have two pairs of sides with the same length and a congruent angle (angles XWY and YWZ are both 90°), both triangles are congruent. THat is, corresponding sides have the same length.
This leads to having sides XY and YZ to be congruent. So we have the equation
first, we add 5 on both sides. So we get
Finally, we divide both sides by 12. We get
Note that
so we have that