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