$2.$ Bob$$s Honey Barn issued a $25-$year, $6\%$ semi$-$annual bond $5$ years ago. The bond currently sells for $105\%$ of its face value. The company$$s tax rate is $40\%.$ Assume the par value of the bond is $$1,000.$

a$.$ What is the pre$-$tax cost of debt?

b$.$ What is the after$-$tax cost of debt?

c$.$ What is more relevant the pre$-$tax or the after$-$tax cost of debt? Why?