Răspuns :
a+b+c=840
a+b=642
b+c=553
642+c=840
c=840-642
c=198
a+553=840
a=840-553
a=287
287+b=642
b=642-287
b=355
Verificare : 287+355+198=840
a+b=642
b+c=553
642+c=840
c=840-642
c=198
a+553=840
a=840-553
a=287
287+b=642
b=642-287
b=355
Verificare : 287+355+198=840