Add $ \dfrac{16}{x^2} $ and $ \dfrac{2}{x^2} $ to get $ \dfrac{18}{x^2} $.

To add expressions with the same denominators, we add the numerators and write the result over the common denominator.

$$ \begin{aligned} \frac{16}{x^2} + \frac{2}{x^2} & = \frac{16}{\color{blue}{x^2}} + \frac{2}{\color{blue}{x^2}} =\frac{ 16 + 2 }{ \color{blue}{ x^2 }} = \\[1ex] &= \frac{18}{x^2} \end{aligned} $$

Divide $ \dfrac{18}{x^2} $ by $ x^2 $ to get $ \dfrac{ 18 }{ x^4 } $.

Step 1: To divide rational expressions, multiply the first fraction by the reciprocal of the second fraction.

Step 2: Multiply numerators and denominators.

Step 3: Simplify numerator and denominator.

$$ \begin{aligned} \frac{ \frac{18}{x^2} }{x^2} & \xlongequal{\text{Step 1}} \frac{18}{x^2} \cdot \frac{\color{blue}{1}}{\color{blue}{x^2}} \xlongequal{\text{Step 2}} \frac{ 18 \cdot 1 }{ x^2 \cdot x^2 } = \\[1ex] & \xlongequal{\text{Step 3}} \frac{ 18 }{ x^4 } \end{aligned} $$