A \(5.0-\mathrm{kg}\) red book is suspended from a spring attached to the ceiling of an elevator that is accelerating downward. Attaching the book causes the spring to stretch \(71 \mathrm{~mm}\) beyond its relaxed length. You also have a yellow book of unknown inertia. When you attach the yellow book and the red one to the spring at the same time, the spring stretches \(110 \mathrm{~mm}\) beyond its relaxed length, When the elevator is at rest, the combination of the two books stretches the spring \(140 \mathrm{~mm}\) beyond its relaxed length.

(a) What is the spring constant?

(b) What is the inertia of the yellow book?

(c) What is the elevator's acceleration?