Hi Lana,
There are expressions for finding the sum of the roots and the product of the roots that your son or daughter probably knows. Thus you can find p + p and pq. The expression you want is
pq^{3} + qp^{3} = pq(q^{2} + p^{2})
Can you see how to find q^{2} + p^{2} if you know pq and p + q?
Penny
