Cho B = {3k + 1 | k ∈ N; k ≤ 3}

To find the elements of the set \( B = \{3k + 1 | k \in \mathbb{N}, k \leq 3\} \), we will substitute values of \( k \) from 1 to 3.

1. For \( k = 1 \):
\[
3(1) + 1 = 3 + 1 = 4
\]

2. For \( k = 2 \):
\[
3(2) + 1 = 6 + 1 = 7
\]

3. For \( k = 3 \):
\[
3(3) + 1 = 9 + 1 = 10
\]

Thus, the set \( B \) includes the elements \( \{4, 7, 10\} \).

None of the provided options (6, 13, 9, 4) fully match the elements of the set. However, 4 is one of the elements of set \( B \).

So, the answer is **4 ∈ B**.