if you want to install gateway on your 3ds check out this tutorial
https://www.youtube.com/watch?v=OHNRtEs9um0
How to play asphalt 3d nitro racing on your 3ds :
1. Download asphalt 3d nitro racing on this site :
http://nitroroms.com/show/file-info/L5191274/Nintendo_3DS/Asphalt_3D_Nitro_Racing_JPN_3DS-BAHAMUT.7z.html
2. Extract Asphalt 3D rom into your Micro SD (if your micro sd is fat32 format it to exFat)
3. after that copy asphalt 3d rom to your micro sd
4. eject your micro sd
5. add your micro sd to your gateway and open your 3ds
6. go to system settings
7. open other settings
8. select profile
9. select Nintendo DS profile
10. you are in gateway mode
11. if you on gateway mode press select and select asphalt 3d nitro racing
12. enjoyed your new game
