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.
Answer:
Step-by-step explanation:
-5/3,-0.5,-1/3,0.5,1.25
Answer:
4
Step-by-step explanation:
-2x- 4 + 5x = 8
Collect like terms
-2x + 5x = 8 +4( when a variable crosses over equality sign it becomes either negative or positive depending on the sign)
3x = 12
Divide via by coefficient of x
X = 12/3
= 4
2r + 2s = 50
2r - s = 17
-----------subtract
3s = 33
s = 11
2r - s = 17
2r - 11 = 17
2r = 28
r = 14
so r = 14 and s = 11
answer is C. r = 14, s = 11