Write a system of equations to describe the situation below, solve using any method, and fill in the blanks.
An event organizer is reserving rooms for two company-wide events. For the quarterly meeting this month, she reserved 3 conference rooms and 5 ballrooms, which can seat a total of 399 attendees. For safety training next month, she reserved 1 conference room and 5 ballrooms, which can seat 363 attendees. How many attendees can each room accommodate?