May: The number of group tickets sold is 3/5*2/3 *a=2a/5.
Ticket revenue is 12*2a/5=24a/5.
The number of retail tickets sold is 1/2* 1a/3=a/6, and the ticket revenue is 16* 1a/6 =8a/3.
June: The group ticket is 4/ 15, and the income is 64a/ 15.
The remaining votes of the retail ticket are a/6, and the income is ax/6.
According to the meaning of the question, it is 24a/5+8a/3=64a/ 15+ax/6.
Solve this equation and get x = 19.2.
Obviously, retail tickets should be priced at each retail ticket 19.2 yuan, so as to make the ticket revenue in these two months even.