Solve the missing items for each independent case. The cost of sales is 60 per cent of sales revenue for each case. (Enter negative amounts using either a negative sign preceding the number, e.g. 45, or parentheses, e.g. (45).) Solve the missing items for each independent case. The cost of sales is 60 per cent of sales revenue for each case. (Enter negative amounts using either a negative sign preceding the number, e.g. 45, or parentheses, e.g. (45).)