notam cu a,b,c cle 3 numere.
a+b+c=3000;
notam cu x numarul cu care se scad cele 3 nr.
a-x=XII=12;
b-x=674;
c-x=2015;
(a-x)+(b-x)+(c-x)=12+674+2014
a+b+c-3x=686+2014
3000-3x=2700
=> 3x=3000-2700
3x=300;
=>x=300:3
x=100;
=> a=12+100
a=112;
b=674+100
b=774;
c=2014+100
c=2114
verificare:112+774+2114=886+2114=3000
