Please assist. Thank you.

11. Dave had some 50-cent coins. Wayne had some $1 coins. Dave gave 50% of his coins to Wayne and Wayne gave 50% of his coins to Dave. Wayne used some of the 50-cent coins to buy a book that cost $5. Dave used some of his $1 coins to buy a bag that cost $16. After that the ratio of the number of 50-cent coins to $1 coin Dave had was 1 : 2 and the number of 50-cent coins to the number of $1 coins Wayne had was 1 : 5.

How much did Dave have at first?