(d) when sales increase by 13%, which of the following should also increase by 13% in a merchandising company? (you may select more than one answer. single click the box with the question mark to produce a check mark for a correct answer and double click the box with the question mark to empty the box for a wrong answer. any boxes left with a question mark will be automatically graded as incorrect.) variable cost checked fixed cost unanswered gross margin checked contribution margin checked net operating income unanswered (e) when sales increase by 13%, which of the following should increase by more than 13% in a merchandising company? (you may select more than one answer. single click the box with the question mark to produce a check mark for a correct answer and double click the box with the question mark to empty the box for a wrong answer. any boxes left with a question mark will be automatically graded as incorrect.) variable cost unanswered fixed cost unanswered gross margin checked contribution margin unanswered net operating income