Answer
$$\frac{74x}{35}$$
Work Step by Step
A common denominator of $5$ and $7$ is $35$, so
$$\frac{7x}{5}+\frac{5x}{7}=\bigg(\frac{7x}{5}\bigg)\bigg(\frac{7}{7}\bigg)+\bigg(\frac{5x}{7}\bigg)\bigg(\frac{5}{5}\bigg)=\frac{49x}{35}+\frac{25x}{35}=\frac{74x}{35}.$$