Chapter 9 - Section 9.4 - Variation and Problem Solving - Exercise Set - Page 663: 24

$0.8$ dollars

Let $C$ be the cost of producing a computer DVD Let $P$ be the number of computer DVDs produced $C=\frac{k}{P}$ $C=1.20; P=4000$ $1.20=\frac{k}{4000}$ $k=4800$ When $P$ is $6000$, $C=\frac{4800}{6000}$ $C=0.8$ dollars