16.

17.

determines how many people have swine in 4 days. But we know that

. Hence, S(4) determines that in 4 days, there are 32 thousands people, who have swine already.
18.

19.

determines that in t days, there are 23 thousands people who have swine already. Since

.

determines that in 3 days, there are 23 thousands people who have swine already.
20.
Watch files.