987,654,321
Nine hundred and eighty-seven million six hundred and fifty-four thousand three hundred and twenty-one.

10,400
ten thousand four hundred （对）
ten thousands four hundreds （错）

345
英式：three hundred and forty-five
美式：three hundred forty five

百万 = million
My hometown has 6 million people.
我家乡有6百万人。

十亿 = billion
The population of China is about 1.3 billion. How about England？
中国人口大概13亿，英国呢？

fractions 分数
2/3的三种方式：
1.two-thirds
2.two over three
3.two divided by three

Generally, in British English we usually connect large numbers with double or single digit figures with and, but in American English and is not used.
通常情况下，英式英语当中，百位和十位要加上and，而在美式英语中不用。
The facial mask brand I use is also used by two-thirds of my friends.
我用的这个面膜牌子，我三分之二的朋友也在用。