There are red balls, yellow balls, and white balls in a pile (the number of each pile is large), each red ball weighs 3 grams, each yellow ball weighs 5 grams, and each white ball weighs 7 grams. Take out 130 grams of balls, the color is not limited , at least how many balls are needed.
有红球、黄球、白球各一堆(每堆数量很多)，每个红球重3克，每个黄球重5克，每个白球重7克，取出130克的球，颜色不限，最少需多少个球．
<result>20</result>