To add or subtract expressions, expand them to make their denominators the same. Least common multiple of $2\left(y+1\right)$ and $2\left(y-1\right)$ is $2\left(y-1\right)\left(y+1\right)$. Multiply $\frac{y+3}{2\left(y+1\right)}$ times $\frac{y-1}{y-1}$. Multiply $\frac{y+1}{2\left(y-1\right)}$ times $\frac{y+1}{y+1}$.
Since $\frac{\left(y+3\right)\left(y-1\right)}{2\left(y-1\right)\left(y+1\right)}$ and $\frac{\left(y+1\right)\left(y+1\right)}{2\left(y-1\right)\left(y+1\right)}$ have the same denominator, subtract them by subtracting their numerators.
To add or subtract expressions, expand them to make their denominators the same. Least common multiple of $2\left(y-1\right)\left(y+1\right)$ and $\left(y-1\right)\left(y+1\right)$ is $2\left(y-1\right)\left(y+1\right)$. Multiply $\frac{3}{\left(y-1\right)\left(y+1\right)}$ times $\frac{2}{2}$.
Since $\frac{-4}{2\left(y-1\right)\left(y+1\right)}$ and $\frac{3\times 2}{2\left(y-1\right)\left(y+1\right)}$ 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 $2\left(y+1\right)$ and $2\left(y-1\right)$ is $2\left(y-1\right)\left(y+1\right)$. Multiply $\frac{y+3}{2\left(y+1\right)}$ times $\frac{y-1}{y-1}$. Multiply $\frac{y+1}{2\left(y-1\right)}$ times $\frac{y+1}{y+1}$.
Since $\frac{\left(y+3\right)\left(y-1\right)}{2\left(y-1\right)\left(y+1\right)}$ and $\frac{\left(y+1\right)\left(y+1\right)}{2\left(y-1\right)\left(y+1\right)}$ have the same denominator, subtract them by subtracting their numerators.
To add or subtract expressions, expand them to make their denominators the same. Least common multiple of $2\left(y-1\right)\left(y+1\right)$ and $\left(y-1\right)\left(y+1\right)$ is $2\left(y-1\right)\left(y+1\right)$. Multiply $\frac{3}{\left(y-1\right)\left(y+1\right)}$ times $\frac{2}{2}$.
Since $\frac{-4}{2\left(y-1\right)\left(y+1\right)}$ and $\frac{3\times 2}{2\left(y-1\right)\left(y+1\right)}$ have the same denominator, add them by adding their numerators.