Assume that capital markets are perfect, then calculate the cost of debt for a group of firms that each are worth $6 million, have a weighted average cost of capital of 19%, and the following equity value and expected return.

Firm A: $1.9 million of equity with a 25% expected return 

Firm B: $2.4 million of equity with a 23% expected return 

Firm C: $2.9 million of equity with a 21% expected return