Domain Analysis: Finding Positive Values of (1/3x-1/6)(-x-4.2)

To find the set of $x$ values where $y = \left(\frac{1}{3}x-\frac{1}{6}\right)\left(-x-4\frac{1}{5}\right)$ is positive, we need to determine where each factor changes sign.

First, find the zeros of the linear factors:

• For $\frac{1}{3}x - \frac{1}{6} = 0$:
  Solving gives $\frac{1}{3}x = \frac{1}{6}$ or $x = \frac{1}{2}$.
• For $-x - 4\frac{1}{5} = 0$:
  Solving gives $-x = -4\frac{1}{5}$ or $x = -4\frac{1}{5}$.

These zeros split the real number line into three intervals. Let's determine the sign of each expression in the intervals:

• Interval $(-\infty, -4\frac{1}{5})$:
  - $\frac{1}{3}x-\frac{1}{6} < 0$ and $-x-4\frac{1}{5} > 0$
• Interval $(-4\frac{1}{5}, \frac{1}{2})$:
  - $\frac{1}{3}x-\frac{1}{6} < 0$ and $-x-4\frac{1}{5} < 0$
• Interval $(\frac{1}{2}, \infty)$:
  - $\frac{1}{3}x-\frac{1}{6} > 0$ and $-x-4\frac{1}{5} < 0$

The product $\left(\frac{1}{3}x-\frac{1}{6}\right)\left(-x-4\frac{1}{5}\right)$ is positive in the interval where both factors are negative or both are positive:

Therefore, the solution is $-4\frac{1}{5} < x < -\frac{1}{2}$, matching with choice 3.