Abigail and Barry are both big fans of the Toronto Raptors. Abigail currently owns tickets for 4 games that haven't yet occurred. Barry has 3 tickets for future games. Assume that all the tickets are for seats at identical locations in the Scotiabank Arena and people can use them for any game they want.

Abigail values her first admission to a Raptors game at $450 and then each additional game in the season is worth $50 less than the previous one. Barry values going to his first Raptors game at $200 and then each additional ticket is worth $20 less than the previous one.

Abigail and Barry are members of a platform, called Ticketraptor, that matches ticketholders and allows them to sell and transfer property of their tickets. Ticketraptor has collected complete data on its users' valuation of the tickets. When matched together by Ticketraptor's algorithm, ticketholders are free to exchange the ticket using the platform at any price they agree to. Users can only agree on one price and they cannot sell multiple tickets with different prices.

A. Ticketraptor is currently not charging any fees in order to attract customers to the service. Abigail and Barry have been matched by Ticketraptor's price for ticket exchange, help ticket raptor find a unique price to recommend to Abigail and Barry for an efficient exchange of tickets

B. How many tickets will be exchanged between Abigail and Barry using the platform ? Explain the reasoning step by step

two questions in total, please provide detailed process and explanation