First, we can convert feet to inches 1 foot=12 inches 7 feet=84 inches Next, we find out inches per hour 84 inches/27 1/2 hours ----------- -------------- 27 1/2 27 1/2 =3.054 inches/hour
Use Hooke's law... (just kidding)
Break down each force vector into horizontal and vertical components.



The resultant force is the sum of these vectors,

and has magnitude

The closest answer is D.
C because you add the angles together
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.