To add or subtract expressions, expand them to make their denominators the same. Least common multiple of $\left(2x-1\right)\left(x+2\right)$ and $\left(x+2\right)\left(x-1\right)$ is $\left(x-1\right)\left(2x-1\right)\left(x+2\right)$. Multiply $\frac{x-1}{\left(2x-1\right)\left(x+2\right)}$ times $\frac{x-1}{x-1}$. Multiply $\frac{3}{\left(x+2\right)\left(x-1\right)}$ times $\frac{2x-1}{2x-1}$.
Since $\frac{\left(x-1\right)\left(x-1\right)}{\left(x-1\right)\left(2x-1\right)\left(x+2\right)}$ and $\frac{3\left(2x-1\right)}{\left(x-1\right)\left(2x-1\right)\left(x+2\right)}$ 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 $\left(2x-1\right)\left(x+2\right)$ and $\left(x+2\right)\left(x-1\right)$ is $\left(x-1\right)\left(2x-1\right)\left(x+2\right)$. Multiply $\frac{x-1}{\left(2x-1\right)\left(x+2\right)}$ times $\frac{x-1}{x-1}$. Multiply $\frac{3}{\left(x+2\right)\left(x-1\right)}$ times $\frac{2x-1}{2x-1}$.
Since $\frac{\left(x-1\right)\left(x-1\right)}{\left(x-1\right)\left(2x-1\right)\left(x+2\right)}$ and $\frac{3\left(2x-1\right)}{\left(x-1\right)\left(2x-1\right)\left(x+2\right)}$ have the same denominator, add them by adding their numerators.
