1. It takes maria eleven hours to fly from Canada to China today.
. =Maria spends eleven hours flying form Canada to China today
解析：
It takes sb some time to do sth 做某事花费某人多长时间
sb spend some time doing sth 某人做某事花费多长时间
2. i don't know how i can swim in the river
=I don't know how to swim in the river. 我不知道怎么样在河里游泳.
how有一个用法是how + to do(即：how + 动词不定式)
Eg：
Can you tell me how to learn English well?
这句话相当于：Can you tell me how I can learn English well?
当省略主语、谓语不至于引起含义不明时,可以直接用how to do来表达.