Answer:
360 screws
Explanation:
First we need to determine how many screws she needs for the 2 decks
We will determine the number of screws for 1 deck
1 deck uses 25 pieces of wood
25 pieces of wood * 8 screws/ piece of wood = 200
200 screws per deck
She is building 2 decks
2 * 200 = 400
400 screws for the 2 decks
She has 40 screws
400 screws she needs - 40 screws she has = 360 screws she still needs