Which of the following statements is incorrect?

The characteristics of preferred stock allow us to use the perpetuity model to estimate the cost of preferred equity.

The after$-$tax cost of equity $($common or preferred. does not have to be adjusted by the marginal income tax rate for the firm.

A firm's risk premium is equal to the weighted average of all its financing costs.

All the answers are correct except one.

The current cost of long$-$term debt if available is the appropriate cost of debt for WACC calculations.