Răspuns :
1000 xa+ 5 x100 +c x10 +9=3 x1000 +b x100 +7x10 +d
1000 xa= 3 x1000
a=3
5 x100=bx100
b=5
c x10=7 x10
c=7
d=9
1000 xa= 3 x1000
a=3
5 x100=bx100
b=5
c x10=7 x10
c=7
d=9