### Corporate Finance : Interest Rate Formula K = R + [ (1.25 X (14 - R)] and Solving for Unknown Variables

I am working on corporate finance and figuring out interest rates. The problem has some of the givens, I need to find the value of the unidentified given. Other examples: 15% = R + [1.25 x (14% - R )] 16% = 9% + [1.10 x (k - 9%)] 15% = 10% + [b x (12.5% - 10%)]