From what height did the body fall, if at the moment when its kinetic energy was equal to potential, it had a speed of 14 m / s.

At the moment when V = 14 m / s: En2 = Ek2.
En2 = m * g * h, where m is the mass of the body, g is the acceleration of gravity (g = 9.8 m / s ^ 2), h is the height of the body when V = 14 m / s.
Ek2 = (m * V ^ 2) / 2, where V is the speed of the body (V = 14 m / s).
m * g * h2 = (m * V ^ 2) / 2.
Then:
h2 = (V ^ 2) / 2g = (14 ^ 2) / (2 * 9.8) = 10 m.
According to the law of conservation of energy:
Ек1 + Еп1 = Ек2 + Еп2, where Eк1 and Eп1 are the energy at the beginning of the fall; Eк2, Eп2-energy when the speed is 14 m / s.
At the beginning of the fall, V = 0 and Eк1 = 0.
En1 = Ek2 + En2.
m * g * h1 = (m * V ^ 2) / 2 + m * g * h2.
h1 = ((V ^ 2) / 2 + g * h2) / g = ((14 ^ 2) / 2) + 9.8 * 10) / 9.8 = 20 m.