Sergio's internet provider charges its customers $8 per month plus 5¢ per minute of on-line usage. Sergio received a bill from the provider covering a 2-month period and was charged a total of $46.50

Sergio's internet provider charges its customers $8 per month plus 5¢ per minute of on-line usage. Sergio received a bill from the provider covering a 2-month period and was charged a total of $46.50. How many minutes did he spend on-line during that period? (Round to the nearest whole minute, if necessary.)