When firm uses information about existing securities $($bonds$,$ preferred and common stocks$)$ to calculate its cost of capital, it's called "weighted average cost of capital".

When a firm uses information about newly issued securities to calculate its cost of capital, it's called "marginal weighted average cost of capital".

For the capital budget decision example, you need to calculate both WACC and marginal WACC.

In this tab, calculate individual costs for existing bonds, preferred and common equity.