Kai sells a small magazine full of celebrity gossip to college students for $2.36 per copy. Hiring the printing press for one day, the only fixed cost, is $494 per issue. The variable cost of printing each issue is $1.20 per copy. The printer tells Kai the cost of hiring the press is to increase by $115 per day. Kai decides to keep his price the same and add colour, increasing variable costs by $0.40 per issue. 

What is the percent increase in unit volume (copies per issue) required to maintain $500 profits and cover the increased fixed and variable costs?