What is the interest during the fifth period (year) if the constant interest rate is 5% and the cash value is 15,000 currency units? The periodic payment is seven years.
一笔现金值为 15000 个货币单位的贷款，固定利率是 5%，第五个还款周期(年份)应支付的利息金额是多少？分期还款的期限是七年。