Price difference in average cost with vendor balance?

price difference in average cost with vendor balance we purchase items withDolar the weighted average cost isDolar then we buy5 items withDolar the weighted average cost isDolar then we return the first item to supplier and will assignDolar which is the current unit cost based on weighted average cost however after returning the goods the vendor balance will not be zero the original price wasDolar and returned withDolar so3Dolar difference. how we solve this in accounting.