$$ 515 g \cdot 2 = 1030 g $$

Combine like terms:

$$ \color{blue}{3g} \color{blue}{-1030g} = \color{blue}{-1027g} $$

Multiply $20$ by $ \dfrac{g}{6} $ to get $ \dfrac{ 20g }{ 6 } $.

Step 1: Write $ 20 $ as a fraction by putting $ \color{red}{1} $ in the denominator.

Step 2: Multiply numerators and denominators.

Step 3: Simplify numerator and denominator.

$$ \begin{aligned} 20 \cdot \frac{g}{6} & \xlongequal{\text{Step 1}} \frac{20}{\color{red}{1}} \cdot \frac{g}{6} \xlongequal{\text{Step 2}} \frac{ 20 \cdot g }{ 1 \cdot 6 } = \\[1ex] & \xlongequal{\text{Step 3}} \frac{ 20g }{ 6 } \end{aligned} $$

Add $-1027g$ and $ \dfrac{20g}{6} $ to get $ \dfrac{ \color{purple}{ -6142g } }{ 6 }$.

Step 1: Write $ -1027g $ as a fraction by putting $ \color{red}{ 1 } $ in the denominator.

Step 2: To add raitonal expressions, both fractions must have the same denominator.
We can create a common denominator by multiplying the first fraction by $\color{blue}{ 6 }$.

$$ \begin{aligned} -1027g+ \frac{20g}{6} & \xlongequal{\text{Step 1}} \frac{-1027g}{\color{red}{1}} + \frac{20g}{6} = \frac{ \left( -1027g \right) \cdot \color{blue}{ 6 }}{ 1 \cdot \color{blue}{ 6 }} + \frac{ 20g }{ 6 } = \\[1ex] & \xlongequal{\text{Step 2}} \frac{ \color{purple}{ -6162g } }{ 6 } + \frac{ \color{purple}{ 20g } }{ 6 }=\frac{ \color{purple}{ -6142g } }{ 6 } \end{aligned} $$