Multiply $ \color{blue}{jx} $ by $ \left( ix+20\right) $ $$ \color{blue}{jx} \cdot \left( ix+20\right) = ijx^2+20jx $$

Multiply each term of $ \left( \color{blue}{ijx^2+20jx}\right) $ by each term in $ \left( ix+10\right) $.

$$ \left( \color{blue}{ijx^2+20jx}\right) \cdot \left( ix+10\right) = i^2jx^3+10ijx^2+20ijx^2+200jx $$

Combine like terms:

$$ i^2jx^3+ \color{blue}{10ijx^2} + \color{blue}{20ijx^2} +200jx = i^2jx^3+ \color{blue}{30ijx^2} +200jx $$

Multiply $250$ by $ \dfrac{ix+2}{i^2jx^3+30ijx^2+200jx} $ to get $ \dfrac{ 250ix+500 }{ i^2jx^3+30ijx^2+200jx } $.

Step 1: Write $ 250 $ as a fraction by putting $ \color{red}{1} $ in the denominator.

Step 2: Multiply numerators and denominators.

Step 3: Simplify numerator and denominator.

$$ \begin{aligned} 250 \cdot \frac{ix+2}{i^2jx^3+30ijx^2+200jx} & \xlongequal{\text{Step 1}} \frac{250}{\color{red}{1}} \cdot \frac{ix+2}{i^2jx^3+30ijx^2+200jx} = \\[1ex] & \xlongequal{\text{Step 2}} \frac{ 250 \cdot \left( ix+2 \right) }{ 1 \cdot \left( i^2jx^3+30ijx^2+200jx \right) } \xlongequal{\text{Step 3}} \frac{ 250ix+500 }{ i^2jx^3+30ijx^2+200jx } \end{aligned} $$