Fill in the missing numbers in the number bonds activity.

Problem Description:

The task involves filling in the missing numbers in a "Number Bonds" worksheet. Number bonds are pairs of numbers that add up to a given total. The goal is to determine the missing number in each bond so that the sum of the two numbers equals the total shown at the top.

Worksheet Layout:

The worksheet is organized into rows and columns, with each circle containing a total (sum) and two smaller circles connected by lines. One of the smaller circles contains a known number, and the other is blank, requiring us to find the missing number.

Step-by-Step Solution:

#### Row 1:
1. First Bond:
- Total: 18
- Known number: 15
- Missing number: \( 18 - 15 = 3 \)
- Filled in: \( 18 = 15 + 3 \)

2. Second Bond:
- Total: 15
- Known number: 12
- Missing number: \( 15 - 12 = 3 \)
- Filled in: \( 15 = 12 + 3 \)

3. Third Bond:
- Total: 19
- Known number: 16
- Missing number: \( 19 - 16 = 3 \)
- Filled in: \( 19 = 16 + 3 \)

#### Row 2:
1. First Bond:
- Total: 13
- Known number: 8
- Missing number: \( 13 - 8 = 5 \)
- Filled in: \( 13 = 8 + 5 \)

2. Second Bond:
- Total: 17
- Known number: 13
- Missing number: \( 17 - 13 = 4 \)
- Filled in: \( 17 = 13 + 4 \)

3. Third Bond:
- Total: 9
- Known number: 4
- Missing number: \( 9 - 4 = 5 \)
- Filled in: \( 9 = 4 + 5 \)

#### Row 3:
1. First Bond:
- Total: 9
- Known number: 12
- Missing number: \( 9 - 12 = -3 \) (This seems incorrect as it results in a negative number. Let's recheck the problem setup or assume a typo.)
- Assuming a typo, if the total were 21 instead of 9:
- Missing number: \( 21 - 12 = 9 \)
- Filled in: \( 21 = 12 + 9 \)

2. Second Bond:
- Total: 11
- Known number: 7
- Missing number: \( 11 - 7 = 4 \)
- Filled in: \( 11 = 7 + 4 \)

3. Third Bond:
- Total: 12
- Known number: 9
- Missing number: \( 12 - 9 = 3 \)
- Filled in: \( 12 = 9 + 3 \)

Final Answer:

After filling in all the missing numbers, the completed worksheet looks like this:

```
Number Bonds
Fill in the missing numbers.

18 = 15 + 3
15 = 12 + 3
19 = 16 + 3

13 = 8 + 5
17 = 13 + 4
9 = 4 + 5

21 = 12 + 9
11 = 7 + 4
12 = 9 + 3
```

Thus, the final answer is:
\[
\boxed{3, 3, 3, 5, 4, 5, 9, 4, 3}
\]