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:
Brad average typing rate in words per minute is 21
1260 divided by 60 = 21
(In case you meant 30 minutes)
1260 divided by 30 = 42
Step-by-step explanation:
In a typing class, the average number N of words per minute typed after t weeks of lessons is
N=157/(1+5.4e^-0.12t)
N=157/(1+5.4e
−
0.12t)
. Find the time necessary to type 75 words per minute