Răspuns :
a+b+c=1989
a+b=1224
c=b+645
c=1989-1224=765
765=b+645
b=120
b+c=?
120+765=885
a=1989-885
a=1104
a+b=1224
c=b+645
c=1989-1224=765
765=b+645
b=120
b+c=?
120+765=885
a=1989-885
a=1104
A+b+c=1989
A+b=1224
C=1989-1224=765
C=645+b
B=765-645=120
A+120=1224
A=1104