Answer:
**each problem is slightly different. See explanations below**
Explanation:
Problem 13. SSS
From the diagram, we're given that ML is congruent to CN. Also, side NL is shared, so side NL is congruent to side LN. We need the third side, so we need MN congruent to CL (tip to shared segment)
Problem 14. SAS
From the diagram, we're given that GF is congruent to XW. Also, angle G is congruent to angle X. To use SAS, we need two sides and the angle between them, so we need a side from each triangle that will "trap" the given angle. Therefore, we need GH congruent to XY (angle vertex to outside)
Problem 15. SSS
From the diagram, we're given that DE is congruent to RS, and EF is congruent to ST. For SSS, we need the third side, so we need DF congruent to RT (vertex touching side II to vertex touching side III)
Problem 16. ASA
From the diagram, we're given that angle C is congruent to angle G, and angle D is congruent to angle H. To use ASA, we need two angles and the side between those two angles, so we need the sides from each triangle that are between the vertices of the two given angles. Therefore, we need CD congruent to GH (side from angle I to angle II)
Problem 17. SAS
From the diagram, we're given that VW is congruent to EF, and WX is congruent to FG. To use SAS, we need two sides and the angle between them, so we need a the angle trapped by the two given sides from each triangle. Therefore, we need angle W congruent to angle F (angle between side I and side II)
Problem 18. ASA
From the diagram, we're given that angle XWV is congruent to angle HWV. Also, the two triangles share side WV, so WV is congruent to WV. To use ASA, we need two angles and the side between those two angles, so we need the other angle from each triangle that will trap the given side. Therefore, we need angle XVW congruent to angle HVW (angle from outside vertex, to shared tip, along shared side)