I : (20/100)*15000 = 2/10* 15000 = 3000 piese in prima etapa
II : (50/100)*(15000-3000) = 5/10* 12000 = 6000 piese in a doua etapa
III: 15000-3000-6000= 6000 piese in a treia etapa
(x/100)* 15000 = 6000
x/100 = 6/15
=> x = 600/15 = 40 %
la c nu-mi dau seama