a)
8 ore . ....................12000 sticle
x ore ....................... 9000 sticle
x = 9000 x 8 : 12000 = 6 ore
b)
8 ore ....................... 6 instalatii
x ore ........................ 4 instalatii
x = 6 : 4 x 8 = 12 ore
c)
12000 : 2 = 6000 st .... 3 inst . in 8 ore
6000 sticle .................. 8 ore
15000 sticle ................. x ore
x = 15000 x 8 : 6000 = 20 ore