Jason bought some bookmarks and gave half to them to Kelvin. Kelvin
bought some stickers and gave half of them to Jason.
Then Jason gave 7 bookmarks to his brother and found that he had 1/9 as
many bookmarks as stickers left. Kelvin gave 12 stickers to his younger
brother and found that he had 1/6 as many bookmarks as stickers left.
(a) How many stickers did Kelvin have in the end?
(b) How many bookmarks did Jason buy?
jason: b-7 = 1/9 s
kelvin: b = 1/6 (s-12)
solve for b and s, and then you want
(a) s-12
(b) b
oops.
(b) Jason bought 2b bookmarks.