28) 13 – 39k + 26p = -13 · ...

28) $$13 – 39k + 26p = -13 \cdot \textbf{(-1+3k-2p)}$$

$$-13 \cdot (-1+3k-2p) = 13 – 39k + 26p$$

Ответ: (-1+3k-2p)