Either the text or the picture need to be corrected.
The example picture says that a resistance 5.2 ohms is ok for a 24v heater cartridge at 30 watts (due to the blue insulated wires shown).
However the text contradicts this for 24v heater cartridge saying that the resistance of a 24v 40 watt heater cart should be about 14.4 ohms or about 19.2 ohms for a 24v 30 watt cart.
The 4.8 ohm resistance of a 12 volt 30 watt heater cart in the text is a closer match to the 5.2 ohms in the picture!
It would be helpful if there was a link to your example replacement X carriage for Prusa i3’s having the required x carriage 45mm Rod Spacing, LM8UU bearings and ~15mm Belt Spacing.