Answer
A publisher wants to spend at most $3000 on printing costs for hardback novels (HN) and paperback novels (PN).
A hardback novel costs $10 per book to print while its paperback version costs only $5 to print.
than means
3000 ≤ HN* 10 + PN* 5
And the second condition
She wants to have at least 400 books on hand.
400 ≥ HN + PN
The system of inequalities that represents the combination of the number of hardback and paperback novels the publisher can print is,
3000 ≤ HN* 10 + PN* 5
400 ≥ HN + PN
o
HN + PN ≤ 400
HN* 10 + PN* 5 ≥ 3000