Using the fact family of $9$9, $9$9, and $18$18.
$+$+ | $=$= | |||
$9$9 | $+$+ | $9$9 | $=$= | $18$18 |
What is $18-9$18−9?
Using the fact family of $6$6, $6$6, and $12$12:
Using the fact family of $8$8, $7$7, and $15$15.
Using the fact family of $5$5, $9$9, and $14$14: