Question

aunt alice gave each of her three nieces a number of silver dollars equal to their ages. the youngest felt that this was unfair. they agreed to redistributed the money. the youngest would split half her silver dollars evenly with the two sisters. the middle sister would then give each of the others 4 silver dollars. finally the oldest was to split half of her dollars equally between the two younger sisters. after exchanging the money each girl had 16 silver dollars. how old were the sisters?
start with each sister having 16 silver dollars and work backwards