If we let each boy or girl have 5u of stickers, when each boy gave away 4/5 of his stickers, means 15 boys gave away 60u of stickers to the 10 girls and so, when distributed evenly among the girls, each girl gets 6u more (than the original 5u she has).
Now each girl has 11u versus each boy has 1u.
So 10u is 10 stickers.
At first, 25 children x 5u = 75 stickers #
(I leave the mathematical equations or model drawing to you)