Motion In A Straight Line

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