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.
X>1 if that helps with your problem
(1/4ab)^-2
Remove negative exponent by rewritten the equation as (4ab)^2
AUse Product rule to get:
4^2a^2b^2
Now raise 4 to the second power to get:
16a^2b^2
The last answer is correct.