1)a+c-d+b=?
bcb7+dc5a=6513
bcb7+dc5a=6513 =) 5257+1256=6513
=)a= 6
b=5
c=2
d=1
2)a-12=b
b-12=c
c-12=d
d-12=21
=)d-12=21
d=21+12
d=33
c-12=d
c-12=33
c=33+12
c=45
b-12=c
b-12=45
b=45+12
b=57
a-12=b
a-12=57
a=57+12
a=69
=) a=69
b=57
c=45
d=33
Succes!! :)
