prima problema :
a=meri
b=peri
a+b=840
a=3*b
(3*b)+b=840
3b+b=840
4b=840
b=840÷4
b=210 peri
a=3*210
a=630 meri
verificare 630+210=840
a doua problema
a+b+c=716
a=b-37
c=b+42
(b-37)+b+(b+42)=716
b+b+b-37+42=716
3b=716+37-42
3b=711
b=711÷3
b=237
a=237-37
a=200
c=237+42
c=279
v: 200+237+279=716