Information Resources, Inc. $($IRI$),$ collects data on consumer packaged goods at

$32,000$ scanner checkout counters and in panel surveys of $70,000$ households. IRI

records indicate that department store$-$brand pantyhose sell for a gross margin of

$43$ percent and a contribution margin of $29$ percent, and the store inventory turns

over $14$ times per year.

a$.$ What expenses explain the difference between $43$ percent and $29$ percent?

b$.$ What percentage change in unit sales is required to increase total contributions if

price is cut by $10$ percent?