12) -0,36p²q + 0,73q²p+ 27/100 pq²-0,64p²q =

Приведем подобные члены:

$$-0.36p^2q + 0.73q^2p + \frac{27}{100}pq^2 - 0.64p^2q = -0.36p^2q + 0.73q^2p + 0.27pq^2 - 0.64p^2q = (-0.36-0.64)p^2q + (0.73 + 0.27)q^2p = -1p^2q + 1q^2p = -p^2q + q^2p$$

Ответ: $$-p^2q + q^2p$$