“General expenses” means the portion of expenses not chargeable specifically to a particular class of insurance which is allocated to earned ocean marine premiums, consisting of that proportion of general or overhead expenses, including salaries of officers and employees, printing and stationery, and taxes of this State and of the United States, which the net premiums of ocean marine insurance written by the insurer bear to the total net premiums from all classes of insurance written by it during the current calendar year.