To find the missing number, we can look for a pattern based on the presented pie charts:

1. **First Pie Chart:**
- Numbers: 5, 6, 15
- Calculation: \(5 + 6 + 15 = 26\)

2. **Second Pie Chart:**
- Numbers: 6, 7, 21
- Calculation: \(6 + 7 + 21 = 34\)

3. **Third Pie Chart:**
- This chart has numbers: 7, 10, ?
- The sum of the known numbers is \(7 + 10 = 17\)
- To find the missing number, we should see how the sums change from the first two:

The pattern suggests that the sum of the two numbers and the missing number increases by a certain value (8 in this case from 26 to 34).

4. If we follow that increase:
- The next total should be \(34 + 8 = 42\).

To find the missing number \(x\):
- \(7 + 10 + x = 42\)
- \(17 + x = 42\)
- \(x = 42 - 17\)
- \(x = 25\)

Thus, the missing number is **25**.