Chapter 1 - Functions and Their Graphs - Section 1.1 Functions - 1.1 Assess Your Understanding - Page 56: 101

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

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