Multiply $ \dfrac{1}{1000} $ by $ x-80 $ to get $ \dfrac{ x-80 }{ 1000 } $.

Step 1: Write $ x-80 $ as a fraction by putting $ \color{red}{ 1 } $ in the denominator.

Step 2: Multiply numerators and denominators.

Step 3: Simplify numerator and denominator.

$$ \begin{aligned} \frac{1}{1000} \cdot x-80 & \xlongequal{\text{Step 1}} \frac{1}{1000} \cdot \frac{x-80}{\color{red}{1}} \xlongequal{\text{Step 2}} \frac{ 1 \cdot \left( x-80 \right) }{ 1000 \cdot 1 } = \\[1ex] & \xlongequal{\text{Step 3}} \frac{ x-80 }{ 1000 } \end{aligned} $$

Multiply $ \dfrac{x-80}{1000} $ by $ x-90 $ to get $ \dfrac{x^2-170x+7200}{1000} $.

Step 1: Write $ x-90 $ as a fraction by putting $ \color{red}{ 1 } $ in the denominator.

Step 2: Multiply numerators and denominators.

Step 3: Simplify numerator and denominator.

$$ \begin{aligned} \frac{x-80}{1000} \cdot x-90 & \xlongequal{\text{Step 1}} \frac{x-80}{1000} \cdot \frac{x-90}{\color{red}{1}} \xlongequal{\text{Step 2}} \frac{ \left( x-80 \right) \cdot \left( x-90 \right) }{ 1000 \cdot 1 } = \\[1ex] & \xlongequal{\text{Step 3}} \frac{ x^2-90x-80x+7200 }{ 1000 } = \frac{x^2-170x+7200}{1000} \end{aligned} $$

Multiply $ \dfrac{x^2-170x+7200}{1000} $ by $ x-85 $ to get $ \dfrac{x^3-255x^2+21650x-612000}{1000} $.

Step 1: Write $ x-85 $ as a fraction by putting $ \color{red}{ 1 } $ in the denominator.

Step 2: Multiply numerators and denominators.

Step 3: Simplify numerator and denominator.

$$ \begin{aligned} \frac{x^2-170x+7200}{1000} \cdot x-85 & \xlongequal{\text{Step 1}} \frac{x^2-170x+7200}{1000} \cdot \frac{x-85}{\color{red}{1}} = \\[1ex] & \xlongequal{\text{Step 2}} \frac{ \left( x^2-170x+7200 \right) \cdot \left( x-85 \right) }{ 1000 \cdot 1 } \xlongequal{\text{Step 3}} \frac{ x^3-85x^2-170x^2+14450x+7200x-612000 }{ 1000 } = \\[1ex] &= \frac{x^3-255x^2+21650x-612000}{1000} \end{aligned} $$

Multiply $ \dfrac{x^3-255x^2+21650x-612000}{1000} $ by $ x-60 $ to get $ \dfrac{x^4-315x^3+36950x^2-1911000x+36720000}{1000} $.

Step 1: Write $ x-60 $ as a fraction by putting $ \color{red}{ 1 } $ in the denominator.

Step 2: Multiply numerators and denominators.

Step 3: Simplify numerator and denominator.

$$ \begin{aligned} \frac{x^3-255x^2+21650x-612000}{1000} \cdot x-60 & \xlongequal{\text{Step 1}} \frac{x^3-255x^2+21650x-612000}{1000} \cdot \frac{x-60}{\color{red}{1}} = \\[1ex] & \xlongequal{\text{Step 2}} \frac{ \left( x^3-255x^2+21650x-612000 \right) \cdot \left( x-60 \right) }{ 1000 \cdot 1 } \xlongequal{\text{Step 3}} \frac{ x^4-60x^3-255x^3+15300x^2+21650x^2-1299000x-612000x+36720000 }{ 1000 } = \\[1ex] &= \frac{x^4-315x^3+36950x^2-1911000x+36720000}{1000} \end{aligned} $$

Add $ \dfrac{x^4-315x^3+36950x^2-1911000x+36720000}{1000} $ and $ 30 $ to get $ \dfrac{ \color{purple}{ x^4-315x^3+36950x^2-1911000x+36750000 } }{ 1000 }$.

Step 1: Write $ 30 $ 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 second fraction by $\color{blue}{1000}$.

$$ \begin{aligned} \frac{x^4-315x^3+36950x^2-1911000x+36720000}{1000} +30 & \xlongequal{\text{Step 1}} \frac{x^4-315x^3+36950x^2-1911000x+36720000}{1000} + \frac{30}{\color{red}{1}} = \\[1ex] &= \frac{ x^4-315x^3+36950x^2-1911000x+36720000 }{ 1000 } + \frac{ 30 \cdot \color{blue}{ 1000 }}{ 1 \cdot \color{blue}{ 1000 }} = \\[1ex] & \xlongequal{\text{Step 2}} \frac{ \color{purple}{ x^4-315x^3+36950x^2-1911000x+36720000 } }{ 1000 } + \frac{ \color{purple}{ 30000 } }{ 1000 } = \\[1ex] &=\frac{ \color{purple}{ x^4-315x^3+36950x^2-1911000x+36750000 } }{ 1000 } \end{aligned} $$