1.My computer is cheaper than yours.
>your computer is not as cheap as mine
2-Lan's bike is cheaper than Nga's bike.
->Nga's bike is more expensive than Lan's bike
3-English is not as difficult as Chinese.
-> Chinese is more difficult than English
4-The Red River isn't as long as the Mekong River.
the Mekong River is longer than The Red River 
5-The weather is hotter this year than it was last year.
The weather last year wasn't as hot as this year