rlg5150 on "Can someone explain this question and answer to me?"

A company has the following target capital structure and costs:
----------Proportion of capital structure-------------Cost of capital
Debt-------------------30%------------------------------------ 10%
Common stock--- 60%---------------------------------- 12%
Preferred stock----10%----------------------------------- 10%

What is the company's weighted-average cost of capital?

Here's what I thought:

Debt: .3 x .1 = .03
Common Stock: .6 x .12 = .072
Preferred Stock: .1 x .1 = .01

.03 + .072 + .01 = 11.2%

10 points to whoever can explain to me the right answer. I'll give you a hint: it's not 11.2%.