sox merge two files of different length

sox merge two files of different length

I have two audio files A of length X and other B of length Y (X > Y). Now
I want to replace the last Y part of file A with the file B.
For e.g. file A is of length 60s and file B is of length 43s. I need to
replace the last 43s of file A with file B.
I hope it is clear.
Is it possible to do this using sox? How, do I need to merge them? If so
then how to merge them?
Also is there any way to automate? Like I don't have to manually determine
the length of both etc.