16.
\(S(4) \text{ it's like t=4, so} \Rightarrow S(4)=9\cdot 4-4=36-4=32\)
17.
\(S(4)\) determines how many people have swine in 4 days. But we know that \(S(4)=32\). Hence, S(4) determines that in 4 days, there are 32 thousands people, who have swine already.
18.
\(S(t)=23 \Rightarrow 23=9t-4 \Rightarrow t=3\)
19.
\(S(t)=23\) determines that in t days, there are 23 thousands people who have swine already. Since \(t=3\). \(S(t)=23\) determines that in 3 days, there are 23 thousands people who have swine already.
20.
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