The problem asks for the number of trees that are taller than 10 m but not more than 20 m. From the given frequency table:

• For the height range $10 < h \leq 15$, the frequency is 13.
• For the height range $15 < h \leq 20$, the frequency is 5.

Adding these frequencies together:

$13 + 5 = 18$

Thus, the number of trees taller than 10 m but not more than 20 m is 18.

Do you have further questions or need details on this calculation?

Here are five related questions to consider:

1. How many trees are taller than 5 m but not more than 15 m?
2. What is the total number of trees recorded in the table?
3. What percentage of trees are between 10 m and 15 m tall?
4. How many trees are either 5 m tall or less than 5 m tall?
5. What is the range of tree heights covered in the table?

Tip: Always double-check the range conditions (e.g., $<, \leq$) to ensure accurate calculations!