Here's the solution:
1. UV = WZ given
2. VW + WX segment addition
3. UV + VW - WX = XY + YZ addition and subtraction property of equality
4. UV + VW + XY + YZ segment addition
5. VW + XY
6. UV - YZ subtraction property of equality
That is how it works:
* For the first blank (1) the answer is 3, 4 or 5 because one of those options was used to go from step 1 to step 3 (addition and subtraction property of equality)
* For the second empty spot (2), the answer is "more than 2 segments were added", because more than 2 segments were added in step 4 (VW,XY and YZ)
* For the third empty spot (3) the answer is "segment addition" because step 2 was obtained by adding a segment (VW+WX)
* The rest of the solution follows from the steps above