50% Common Stock, 5% preferred stock, 45% debt, cost of equity is 14%
cost of preferred stock is 6% and cost of debt is 7.5% Relevant tax
rate is 35%

Hi!!

The WACC's formula is:

WACC = Wd*rD*(1-T) + Ws*rS + Wp*rP;

where:
Wd = weight of debt
Ws = weight of common stocks
Wp = weight of preferred stocks
Wd + Ws + Wp = 1
rD = cost of debt 
rS = cost of common stocks
rP = cost of preferred stocks
T = tax rate

In this case we have:
Wd = 0.45
Ws = 0.5
Wp = 0.05
Wd + Ws + Wp = 1
rD = 7.5% 
rS = 14%
rP = 6%
T = 0.35

Then:
WACC = Wd*rD*(1-T) + Ws*rS + Wp*rP =
     = 0.45*7.5%*0.65 + 0.5*14% + 0.05*6% =
     = 9,49375 %


See for additional reference:
"Weighted Average Cost of Capital - WACC":
http://www.investopedia.com/terms/w/wacc.asp

"WACC - Weighted Average Cost of Capital":
http://www.valuebasedmanagement.net/methods_wacc.html


Search strategy:
WACC formula


I hope this helps you. 

Regards,
livioflores-ga