Answer:
4.2
Step-by-step explanation:
f varies inversly with L can be translated matimatically as:
β f = k/L
It takes 7 pounds of pressure to break a 3 feet long board.
Replace f by 7 and L by 3.
β 7 = k/3 => k=7Γ3=21
β β β β β β β β β β β β β β β β β β β β β β β β β β
Let's find tge length of a board that takes 5 pounds of pressure to be broken.
β 5 = k/L
β 5 = 21/L
β L = 21/5 = 4.2
So the board is 4.2 feet long