Answer:
- a. What is the company’s WACC? 
 R_Wacc =  13% (65%) + 5% (5%) + 6% (30%) * (1-0,25) =  10,05%
- b. What is the aftertax cost of debt?
 The aftertax cost of debt is:    
 R_Debt :  (1 - 0,25) x 6% = 4,50%
Explanation:
The WACC it's defined by the formula :
WACC: E/V*Re + D/V*Rd *(1-0,25)
 Re:  	13,00%  Cost of Common Equity    
 Re:  	5,00%  Cost of Preferred STOCK  
 Re:  	6%     Cost of Debt  
 E/V:  	65%   Percentage of financing that is Common Equity  
 PS/V:  	5%     Percentage of financing that is Preferred Stock  
 DB/V:  	30%    Percentage of financing that is Debt  
 Tax:  25%    Corporate tax rate  
Now we have all of the components to calculate the WACC. 
The WACC is:      	
R_Wacc =  13% (65%) + 5% (5%) + 6% (30%)*(1-0,25) =  10,05%  
The aftertax cost of debt is:    
R_Debt :  (1 - 0,25) x 6% = 4,50%