An earthquake causes a 3 kg book to fall from a shelf. if the book lands with a speed of 4.0 m/s, from what height did it fall?

Given:
3kg book
speed of falling of 4.0 m/s
acceleration due to gravity -9.8 m/s² 

Vf² = Vi² + 2 * a * d

Vf = final velocity ; Vi = initial velocity ; a = acceleration ; d = distance

0² = (4 m/s)² + 2(-9.8m/s²) * d
0 = 16 m²/s² -19.6 m/s² * d
-16 m²/s² = -19.6 m/s² * d
-16 m²/s²  / -19.6 m/s² = d
 0.82 m = distance

The 3 kg book fell from the a shelf at the height of 0.82 meters.