CIV why discount with wacc and not cost of equity?

Hello,

In example 4 of chapter 14, in order to calculate WIC, we divide by wacc and not cost of equity. Why is that? It seems that the earnings before tax we calculated do include interest expense.
So we are discounting earnings after interest by a rate of return that is an average of the expectation of the equity and debt holder.

It doesn’t make sense to me.