3 kg smantana ............27 l lapte
1 kg smantana ............27 : 3 = 9 l lapte
20 kg smantana ........ 9 × 20 = 180 l lapte
10 kg unt ........... 180 l lapte
1 kg unt ............ 180 : 10 = 18 l lapte
90 kg unt ........ 18 × 90 = 1 620 litri lapte
raspuns:
1 620 litri lapte