a x (b+c)=a x b+a x c, stiim ca a x c=4000 si b= 10, atunci inlocuim valorile
ax10+4000=6000
10a=6000-4000
10a=2000
a=2000:10
a=200
ex 2
a-b=3550, c=1800, 2a-2b-3c=?
2a-2b-3c= 2(a-b)-3c=2x3550-3x1800=7100-5400=17
