Solution:

Every number has 2 neighbors. What comes before the number is called the small neighbor; it's 1 less than the number. What comes after the number is called the big neighbor; it's 1 more than the number. 6 is 1 less than 7, so 6 is the small neighbor of 7. 8 is 1 more than 7, so 8 is the big neighbor of 7.
To find a 2-digit number's small neighbor and big neighbor, we can look at the last digit. For example, the last digit of 56 is 6. The number that comes before 6 is 5, so the small neighbor of 56 is 55. The number that comes after 6 is 7, so the big neighbor of 56 is 57. Similarly, the small neighbor of 58 is 57 and the big neighbor of 58 is 59.

Solution:

1. The small neighbor of 9 is 8; the big neighbor of 9 is 10. Do you know that the number in between plus itself is equal to its small neighbor plus its big neighbor? Let's calculate and see. 9 plus 9 equals 18; 8 plus 10 equals 18, too! The correct equation is 8+10=18. Remember, the number in between plus itself is equal to its small neighbor plus its big neighbor.
2. The big neighbor of which number is 15? If a number's big neighbor is 15, that number must be 1 less than 15. So, the number is 15-1=14. The number in between is 14. Now, let's figure out what comes before 14, or the small neighbor of 14. The small neighbor of 14 is 14-1=13. Fill 13 in the blank to the left of 14. The correct equation is 14-1=13.