What are the interest payments at a yearly interest rate of 5.5 %, a monthly payment period for 2 years and a current cash value of 5,000 currency units? The start period is the 4th and the end period is the 6th. The payment is due at the beginning of each period.
如果一项贷款的当前现金值是 5,000 货币单位，年利率为 5.5%，偿还期限为 2 年，按月支付，且分期支付额在一个周期的开始时到期，则第 4 至第 6 个周期内的利息总额是多少？