A clothing store sells a kind of clothing. If the price of each piece is 500 yuan, then 60% of the selling price is the purchase price, and 40% of the selling price is the money earned. Now we want to engage in promotional activities, in order to ensure that the money earned for a piece of clothing is not less than 150 yuan. How should the discount be determined?
服装店卖一种服装，如果每件售价500元，那么售价的60%是进价，售价的40%就是赚的钱．现在要搞促销活动，为保证一件衣服赚的钱不少于150元．应该怎样确定折扣？
<result>150</result>