Final answer:
The subject of this question is Mathematics, specifically the concept of variables and algebraic expressions. The expression h = x(2x + 1) allows us to calculate the total number of items (hats) based on the number of helmets (x) using algebraic operations.
Step-by-step explanation:
The subject of this question is Mathematics, and specifically the concept of variables and algebraic expressions.
In the given expression h = x(2x + 1), the variable x represents the number of helmets. The expression allows us to calculate the total number of items (hats) based on the number of helmets (x) using algebraic operations.
For example, if x = 3, we can substitute it into the expression: h = 3(2 * 3 + 1) = 3(6 + 1) = 3(7) = 21. So, if there are 3 helmets, there will be 21 hats.