Total cost is equal to the sum of

The correct answer is A. Fixed cost + variable cost.

Fixed costs are costs that do not change with the level of production, such as rent, insurance, and salaries. Variable costs are costs that change with the level of production, such as the cost of raw materials and labor. Total cost is the sum of fixed costs and variable costs.

B. Average cost is the total cost divided by the number of units produced. C. Marginal cost is the change in total cost that results from producing one more unit. D. Transportation expense and installation cost are examples of variable costs.