Multiply $ \dfrac{49}{4} $ by $ k $ to get $ \dfrac{ 49k }{ 4 } $.

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

Step 2: Multiply numerators and denominators.

Step 3: Simplify numerator and denominator.

$$ \begin{aligned} \frac{49}{4} \cdot k & \xlongequal{\text{Step 1}} \frac{49}{4} \cdot \frac{k}{\color{red}{1}} \xlongequal{\text{Step 2}} \frac{ 49 \cdot k }{ 4 \cdot 1 } = \\[1ex] & \xlongequal{\text{Step 3}} \frac{ 49k }{ 4 } \end{aligned} $$

Multiply $ \dfrac{49k}{4} $ by $ 2 $ to get $ \dfrac{ 98k }{ 4 } $.

Step 1: Write $ 2 $ as a fraction by putting $ \color{red}{ 1 } $ in the denominator.

Step 2: Multiply numerators and denominators.

Step 3: Simplify numerator and denominator.

$$ \begin{aligned} \frac{49k}{4} \cdot 2 & \xlongequal{\text{Step 1}} \frac{49k}{4} \cdot \frac{2}{\color{red}{1}} \xlongequal{\text{Step 2}} \frac{ 49k \cdot 2 }{ 4 \cdot 1 } = \\[1ex] & \xlongequal{\text{Step 3}} \frac{ 98k }{ 4 } \end{aligned} $$

Subtract $ \dfrac{98k}{4} $ from $ 7k $ to get $ \dfrac{ \color{purple}{ -70k } }{ 4 }$.

Step 1: Write $ 7k $ as a fraction by putting $ \color{red}{ 1 } $ in the denominator.

Step 2: To subtract raitonal expressions, both fractions must have the same denominator.
We can create a common denominator by multiplying the first fraction by $\color{blue}{ 4 }$.

$$ \begin{aligned} 7k- \frac{98k}{4} & \xlongequal{\text{Step 1}} \frac{7k}{\color{red}{1}} - \frac{98k}{4} = \frac{ 7k \cdot \color{blue}{ 4 }}{ 1 \cdot \color{blue}{ 4 }} - \frac{ 98k }{ 4 } = \\[1ex] & \xlongequal{\text{Step 2}} \frac{ \color{purple}{ 28k } }{ 4 } - \frac{ \color{purple}{ 98k } }{ 4 }=\frac{ \color{purple}{ -70k } }{ 4 } \end{aligned} $$

Subtract $28k$ from $ \dfrac{-70k}{4} $ to get $ \dfrac{ \color{purple}{ -182k } }{ 4 }$.

Step 1: Write $ 28k $ as a fraction by putting $ \color{red}{ 1 } $ in the denominator.

Step 2: To subtract raitonal expressions, both fractions must have the same denominator.
We can create a common denominator by multiplying the second fraction by $\color{blue}{4}$.

$$ \begin{aligned} \frac{-70k}{4} -28k & \xlongequal{\text{Step 1}} \frac{-70k}{4} - \frac{28k}{\color{red}{1}} = \frac{ -70k }{ 4 } - \frac{ 28k \cdot \color{blue}{ 4 }}{ 1 \cdot \color{blue}{ 4 }} = \\[1ex] & \xlongequal{\text{Step 2}} \frac{ \color{purple}{ -70k } }{ 4 } - \frac{ \color{purple}{ 112k } }{ 4 }=\frac{ \color{purple}{ -182k } }{ 4 } \end{aligned} $$