To add or subtract expressions, expand them to make their denominators the same. Least common multiple of $\left(x^{3}\right)^{8}$ and $x^{4}$ is $x^{24}$. Multiply $\frac{1}{x^{4}}$ times $\frac{x^{20}}{x^{20}}$.
$$\frac{1^{8}}{x^{24}}+\frac{x^{20}}{x^{24}}$$
Since $\frac{1^{8}}{x^{24}}$ and $\frac{x^{20}}{x^{24}}$ have the same denominator, add them by adding their numerators.
To add or subtract expressions, expand them to make their denominators the same. Least common multiple of $\left(x^{3}\right)^{8}$ and $x^{4}$ is $x^{24}$. Multiply $\frac{1}{x^{4}}$ times $\frac{x^{20}}{x^{20}}$.
$$\frac{1^{8}}{x^{24}}+\frac{x^{20}}{x^{24}}$$
Since $\frac{1^{8}}{x^{24}}$ and $\frac{x^{20}}{x^{24}}$ have the same denominator, add them by adding their numerators.
