d. \( R=W+r R \quad \) for \( R \)

To solve for \( R \) in the equation \( R = W + r R \), you can first isolate \( R \) on one side. Start by rearranging the equation: subtract \( r R \) from both sides to get \( R - r R = W \). Factor out \( R \) to yield \( R(1 - r) = W \). Finally, divide both sides by \( (1 - r) \) to find \( R = \frac{W}{1 - r} \). Now you have the formula! You can easily plug in any values for \( W \) and \( r \), as long as \( r \) is not equal to 1, ensuring \( R \) remains defined. Happy calculating!