You cannot "convert" a RAR to an MP3 because the RAR is just a box holding the files. You need to open the box first. Use a free tool like 7-Zip or the official WinRAR to extract the contents.
: They have downloaded a music album or a podcast that is compressed in a .rar file and need to get the .mp3 files out. rar v mp3 skachat
Usually, when people search for "rar v mp3 skachat" (RAR to MP3 download), they are trying to do one of two things: You cannot "convert" a RAR to an MP3