please help me answer 3,4,5 thanks

3) The before-tax cost of debt, which is higher than the after-tax cost, is used as the component cost of debt for purposes of developing the firm's WACC. a True b.False The cost of debt is equal to one plus the marginal tax rate multiplied by the interest rate on new debt 4) a. True b. False 5) If a firm's marginal tax rate is decreased, this would, other things held constant, lower the cost of debt used to calculate its WACC. a True b. False