In counties having a population of more than 13,700 and less than 13,800 inhabitants, or a population of more than 29,000 and less than 30,000 inhabitants, according to the last preceding Federal Census, and in counties having a population of more than 46,000 and less than 47,000 inhabitants, according to the last preceding Federal Census, the first assistant to the county superintendent of public instruction is entitled to receive an annual salary of not more than $5,500; however, the aggregate salaries of all assistants to the county superintendent may not exceed $8,800 a year.