When Musa and Kamal were studying overseas Musa borrowed from Kamal $ 1000 USD. At that time the exchange rate was: USD 1 = RM 2.5. Later, when both returned to Malaysia, Kamal borrowed RM 2000 from Musa and the rate was USD 1 = RM 3. And today, when the rate is USD 1 = RM 4 they want to settle their debts through Muqassah. Identify the type of muqassah contract that they should use and advise them on the correct solution.