How many payment periods does a payment period cover with a periodic interest rate of 6%, a periodic payment of 153.75 currency units and a present cash value of 2.600 currency units.
一笔贷款的当前现金值是 2600 货币单位，每个还款期的利率是 6%，还款金额是 153.75 货币单位，要用几个还款期才能偿清呢？