a+b=3(a-b)
(a+b)+(a-b)=320=>(a+b)=320-(a-b)
320-(a-b)=3(a-b)
320-(a-b)-3(a-b)=0
320-a+b-3a+3b=0
320-4a+4b=0
-4a+4b=320
-a+b=80
a-b=80
a+b=3(a-b)
a+b=3*80=>a+b=240 =>a=240-b
a-b=80
240-b-b=80<=>240-2b=80<=>240-80=2b<=>160=2b<=>b=160:2=>b=80
a=240-80=>a=160
Verificare
(a+b)+(a-b)=320
(160+80)+(160-80)=240+80=320