Mark bought some erasers and gave half of them to Susan.
Susan bought some stickers and gave half of them to Mark.
Mark sold 6 stickers and Susan sold 10 erasers.
The number of stickers Mark had in the end became 1/5 of the
number of erasers that he had in the end.
The number of stickers that Susan had in the end became 1/3 of
the number of erasers that she had in the end.
How many stickers did Susan buy?
so Mark started with m erasers
Susan started with s stickers
s/2 - 6 = 1/5 (m/2)
s/2 = 1/3 (m/2 - 10)
solve for s