mp4 is a video program format.
mp3 is a audio program format.
However, it is normal to have both audio and video on mp4 recordings.

I belive that mp4 is video format which use a mp3 sound anyway so i think yes it will play mp3

Depending on how it was programmed, your MP4 player should recognize MP3 format because it's a standard. If it doesn't, then you might need to download an add-on to the media player so that it recognizes MP3s.

Thanks soo much for all your help. Finally i get a straight answer :)