Final answer:
Total sales revenue and total variable costs vary with the number of units sold and are therefore a function of Q in the profit equation, while total fixed costs are not.
Step-by-step explanation:
In the profit equation, total sales revenue and total variable costs are a function of the number of units sold (Q). Total sales revenue is calculated by multiplying the price per unit by the quantity of units sold, reflecting the overall income generated from sales. On the other hand, total variable costs vary with the production level or quantity of units produced and sold; they are the sum of costs that are incurred proportional to the quantity of output. Despite being part of total costs, total fixed costs do not vary with the number of units sold, hence they are not a function of Q.