Chapter R - Elementary Algebra Review - R.4 Polynomials - R.4 Exercise Set - Page 961: 42

$12$

Substituting $p$ with $-4$ and $q$ with $-2$, the given expression, $ 2pq^3-5q^2+8p ,$ evaluates to \begin{array}{l}\require{cancel} 2(-4)(-2)^3-5(-2)^2+8(-4) \\\\= 2(-4)(-8)-5(4)+8(-4) \\\\= 64-20-32 \\\\= 12 .\end{array}