what is the formula to Estimate the firm$$s before$-$tax and after$-$tax component cost of debt $.$The effective tax rate is $28\mathrm{.}92\%.$ Interest Expense $1,973,000,000$

Total Debt $$49,895,000,000\mathrm{.}00.$ Not sure if interest expense is needed. Please show me the formulas and also show them written out in Excel or with math mode because I can't understand when it's just typed out it confuses me$.$ Free to use hypothetical numbers if I gave the wrong information I just need to understand where to find the information that is needed to calculate the formula, and then to know what that formula is$.$