Kai sells a small magazine full of celebrity gossip to college students for $2.06 per copy. Hiring the printing press for one day, the only fixed cost, is $301 per issue. The variable cost of printing each issue is $0.86 per copy. The printer tells Kai the cost of hiring the press is to increase by $121 per day. Before the increase in the cost of hiring the press, Kai was earning a profit of $500 per issue.

How many copies per issue (units) was Kai selling?