A horse rider covers half the distance with \(5 \, \text{m/s}\) speed. The remaining part of the distance was travelled with speed \(10 \, \text{m/s}\) for half the time and with \(15 \, \text{m/s}\) for other half of the time. The mean speed of the rider averaged over the whole time of motion is \( \frac{x}{7} \, \text{m/s} \). The value of \( x \) is _______.