Here's a sample question. I know the answer, I just don't know how to get to the answer!

"Corp. is investing in a major capital budgeting project that will require the expenditure of $10 million. The money will be raised by issuing $3 million of bonds, $1 million of preferred stock, and $6 million of new common stock. The company estimates is after-tax cost of debt to be 6%, its cost of preferred stock to be 8%, the cost of retained earnings to be 12%, and the cost of new common stock to be 15%. What is the weighted average cost of capital for this project?"

ANSWER

"Weighted average cost of capital (WACC) for the project is as follows:

Percentage Cost WACC
Bond - $3million 30% 6% 1.8%
Preferred stock - $1million 10% 8% 0.8%
New Common Stock - $6million 60% 15% 9.0%
Total $10miilion 100% 11.6%

Therefore, WACC for the project is 11.6%"

My exact question is, where did the numbers 1.8% 0.8% and 9.0% come from? (Also, why was the 12% cost of retained earnings thrown into the question? Does that have anything to do with the answer?)