#### Answer

$H(x) = P(x) \cdot I(x)$

#### Work Step by Step

Since the percentage of income spent on healthcare (P($x$)) times the income (I($x$)) would give the total expenditure on healthcare (H($x$)), H($x$) can be expressed by the product of $P(x)$ and $I(x)$.:
$H(x) = P(x) \cdot I(x)$