In the supermarket, fruit candy sells for 20 yuan per kilogram, milk candy sells for 25 yuan per kilogram, and chocolate candy sells for 30 yuan per kilogram. One morning, a total of 20 kilograms of these three kinds of sugar were sold, and the total income was 480 yuan. It is known that the toffee and chocolate candy are sold for a total of 300 yuan. May I ask: how many kilograms of toffee are sold?
超市里，水果糖每千克卖20元，奶糖每千克卖25元，巧克力糖每千克卖30元．某天上午，这三种糖一共卖了20千克，总收入是480元．已知奶糖和巧克力糖总共卖了300元，请问：其中卖出奶糖多少千克？
<result>6</result>