abc:cba=3 rest 126.
Deci abc=cba*3+126
a-c=4
Deci a=c+4
Înlocuim si transformam in baza 10 astfel: 100a+10b+c=(100c+10b+a)*3+126
100(c+4)+10b+c=300c+30b+3(c+4)+126
101c+10b+400=303c+30b+12+126/-101c-10b-138
262=202c+20b/:2
131=101c+10b
Pana aici am reusit :)