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Text Solution:

Since x³ is the highest (really, only) power of the base x, and since y⁷ is the highest (only) power of the base y, the LCD of these two fractions is (x³)(y⁷). Let’s convert each fraction to a denominator of (x³)(y⁷) and combine the fractions:

$\begin{array}{l}\Rightarrow \frac{y^7}{y^7}\left(\frac{1}{x^3}\right)+\frac{x^3}{x^3}\left(\frac{1}{y^7}\right)\\ \Rightarrow \frac{y^7}{x^3{y}^7}+\frac{x^3}{x^3{y}^7}=\frac{x^3+y^7}{x^3{y}^7}\end{array}$