caiete=a,creioane=b , 7a-4b=100.000-2.2000. 7a+4b=100.000-4000. 7a+4b=96.000lei. 7a=28b. 7a+4b=96000. 28b+4b=96000. 32b=96000lei. 1b=96000÷32. 1b=3000lei. 7a+4b=96000. 7a+4×3000=96000. 7a+12000=96000. 7a =96000-12000. 7a=84000. a=84000÷7. a=12000. proba: 7a+4b=96000lei. 7×12000+4××3000=96000. 96000=96000