the number of wavelength in transmission line

A building is wired with 10MHz Ethernet cable. Assuming a velocity of propagation 20 cm per nanosecond.

The number of wavelength of the 10MHz signal = 30m/20m = 1.5

what does it mean 1.5?

I can calculate the number of wavelenght, but I don't know what does it mean.

thanks

For a data cable, the calculation doesn't mean anything. First point is, you have no 10 MHz sine wave with ethernet signaling but a complex pulse pattern. Second point is, you have termination at both ends and (hopefully) not standing waves. Thus signal delay is the most interesting cable property, furthermore frequency dependant attenuation, appearing as pulse distortion here.

It only means that the cable is 1.5 lambda.
Or in other words, the phase of the signal
does not change.

As mentioned above, this number means nothing usable in ethernet cable. In some point of view, it can be interpreted as an electric length of this cable, which is in this case 1,5*360 deg = 540 degrees or 3 pi.