Answer
$0.8$ dollars
Work Step by Step
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