depends on the balance sheet data given by the question, if the data is comprehensive and separates debt from other liabilities, you use debt.
if the data only gives you “total liabilities”, you use it. don’t assume anything. read the questions and the vignette carefully. there might be small clues such as “X has estimated that 95% of total liabilities to be interest-bearing debt” or “management has indicated that the current capital structure is optimal and is equal to their target D/E of something something”