ONE WAY TO THINK ABOUT IT
Use a double and one more group.
3 × 6 = 2 × 6 + 6 = 12 + 6 = 18. Keep all three equal groups visible.
Try this together
Build three rows, hide one and work from the double.
Say the complete fact, draw or build its groups, then try it again without the picture. It is fine to return to a known fact when an answer feels uncertain.