3abc=3000+ax100+bx10+c
abc3=ax1000+bx100+cx10+3
0<= a,b,c <= 9
(abc3)x3+4=3abc
(ax1000+bx100+cx10+3)x3+4=3000+ax100+bx10+c
ax3000+bx300+cx30+9+4=3000+ax100+bx10+c
ax(3000-100)+bx(300-10)+cx(30-1)=3000-13
ax2900+bx290+cx29=2987
29x(ax100+bx10+c)=2987
ax100+bx10+c=2987:29=103
numarul abc=103
a=1, b=0, c=3