## Precalculus (6th Edition)

$\dfrac{13x}{20}$
Make the rational expressions similar by using their LCD of $20$ to obtain: $\dfrac{2x}{5}+\dfrac{x}{4} \\=\dfrac{2x\color{magenta}{(4)}}{5\color{magenta}{(4)}}+\dfrac{x\color{magenta}{(5)}}{4\color{magenta}{(5)}} \\=\dfrac{8x}{20}+\dfrac{5x}{20} \\=\dfrac{8x+5x}{20} \\=\dfrac{13x}{20}$