Because a firm cannot change the amounts of its fixed inputs used in the short run, it has to use more of its variable inputs to increase production. That means that the firm has to pay more for variable inputs to increase output. The sum of all variable costs a firm pays for variable inputs is called the total variable cost (TVC). Since labor is the only variable input for our representative firm, its total variable cost will be the wage rate times the amount of labor used. Thus the formula would be this: Total Variable (TVC) = Wage (w) x Labor (L). The correct answer is B.