So at first, Jenny already has 150 more stickers than Helen.
Now that Helen gives her 270 of her stickers, she loses 270 stickers
So now Jenny has 150+270= 420 stickers more than Helen
Question states that now Jenny has 4 times more stickers than Helen
Drawing model, Jenny has 4 parts and Helen has 1 part, they have a difference of 3 parts
Hence 3 parts is equal to 420 stickers, 1 part is 420/3 = 140 stickers.
Jenny has 140×4= 560 stickers at first