Answer:
Step-by-step explanation:
We have been given that Niu has decorated x cards. He started with 24 stickers and he used 4 stickers per card. So stickers used in x cards will be 4x.
As initial number of stickers was 24, so we can find number of stickers left after decorating x cards by subtracting number of stickers used in x cards from 24.
Therefore, the expression will represent the number of stickers that Niu has left after decorating x cards.