Factor the four-term polynomial.
pq - 3r + pr - 3q.
(p - 3)(q + r)
(p - r)(q + 3)
(p + 3)(q - r)
pq - 3r + pr - 3q.
(p - 3)(q + r)
(p - r)(q + 3)
(p + 3)(q - r)