A soil having the average properties, bulk unit weight $=19\ \text{kN/m^3$, angle of internal friction $=25^\circ$ and cohesion $=15\ \text{kPa}$, is being formed on a rock slope at an inclination of $35^\circ$ with the horizontal. The critical height (in m) of the soil formation up to which it would be stable without failure is \underline{\hspace{2cm}} (round off to one decimal place).
[Assume the soil is formed parallel to the rock bedding plane and there is no ground water effect.]}