24X is the paired TACAN channel. It's paired (permanently associated) with 108.7 MHz (localizer frequency for LTAF) and 330.5 MHz (Glide Slope). See this reference. (Scroll down to see the table)
So, if I tune in the localizer frequency (108.7 MHz at LTAF) my ILS navigation equipment would automatically also tune in 330.50 MHz (the Glide Slope frequency) and, if my nav equipment also included a DME unit, I would see my distance from the DME facility, which looks like it is at the same location as the Glide Slope antenna at LTAF. If, for some reason, I did not have a separate DME unit in the aircraft, but had a separate TACAN nav unit, I could set the TACAN channel to 24X (which tunes in the DME interrogation frequency of 1048 MHz and a reply frequency of 985 MHZ) and would be able to access the DME through the TACAN unit.
There is only azimuth guidance (in addition to distance/DME info) from a TACAN unit when navigating to/from a VORTAC or TACAN station, which is not at issue in your question.
I've merged the column headings in the image below with the reference for Channel 24X.