谁能解释一下这句话是什么意思？

此为PREP P1 106题正确选项的句子

Officials at the United States Mint believe that the Sacagawea dollar coin will be used as a substitute for four quarters more than for the dollar bill because it weighs only 8.1 grams, far less than four quarters, which weigh 5.67 grams each.

1.什么叫FOUR QUARTERS?

2.SACAGAWEA DOLLAR中8.1克，比FOUR QUARTERS（每个5.67克）远远的轻，这是啥意思

难道这个5.67克指的是1 QUATER的重量，然后4 QUATERS就有20多克，比1 SACAGAWEA DOLLAR重？

谢了LS

不过对于中间那个比较（ a substitute for four quarters more than for the dollar bill ），FOR 4个25分和 FOR DOLLAR BILL比较，这里是什么意思啊