They are essentially asking us to solve:

Solving this equation for x tells us that it will take around 80.1 years for the materials in the vault to reduce to 357 pounds.
Can you post the scale drawing please so I can help you
Answer: Associative property
Step-by-step explanation: it is the same equation but they switched the numbers around on the other side of the equal sign so therefore its associative property
The answer to this questions is 70kg.