What is the formula for computing the internal growth rate $($IGR$)?$

$\frac{\text{R}\text{O}\text{E}b}{1-\text{R}\text{O}\text{E}{b}^{\text{'}}}$

$\frac{\text{R}\text{O}\text{A}b}{1-\text{R}\text{O}\text{A}b}$

$\frac{\text{R}\text{O}\text{A}+b}{1-\text{R}\text{O}\text{A}b}$

$\frac{\text{R}\text{O}\text{A}b}{1+\text{R}\text{O}\text{A}b}$