Answer
in approximately $23.25 \text{ years after the year } 2000$
Work Step by Step
Given that
\begin{array}{l}\require{cancel}
w=-2.11t+69.2
\\\text{and}\\
s=-0.42t+29.9
,\end{array}
then $s\gt w$ is equivalent to
\begin{array}{l}\require{cancel}
-0.42t+29.9\gt-2.11t+69.2
.\end{array}
Using the properties of inequality, then
\begin{array}{l}\require{cancel}
-0.42t+2.11t\gt69.2-29.9
\\\\
1.69t\gt39.3
\\\\
t\gt\dfrac{39.3}{1.69}
\\\\
t\gt23.254437869822485207100591715976
.\end{array}
Hence, the consumption of skim milk will be greater than the consumption of whole milk after approximately $
23.25 \text{ years after the year $2000$}
.$
