$$P - 2,\,\,Q - 1,\,\,R - 7,\,\,S - 6$$

$$P - 6,\,\,Q - 3,\,\,R - 4,\,\,S - 4$$

$$P - 4,\,\,Q - 1,\,\,R - 6,\,\,S - 2$$

$$P - 3,\,\,Q - 4,\,\,R - 6,\,\,S - 7$$