\[f(x) = - \frac{1}{3}x + 2\]
\[f(x) = 4:\]
\[4 = - \frac{1}{3}x + 2\]
\[\frac{1}{3}x = 2 - 4\]
\[\frac{1}{3}x = - 2\]
\[x = - 2\ \ :\frac{1}{3} = - 2 \cdot 3\]
\[x = - 6.\]