1. I haven't gone to the supermarket for three weeks.
-> The last time I went to the supermarket was three week ago.
2. It often takes me thirty minutes to walk to school.
-> I often spend thirty minutes (on) walking to school.
4. I worker very hard for the exam. Then I passed it.
-> Before I passed the exam. I had worked very hard for it.
5. It takes Minh 2 hours to do his homework everyday.
-> Minh spends 2 hours doing his homework every day.
6. I haven't heard from them for ages.
-> it's ages since I (last) heard from them
7. I tookva shower. I went to bed.
-> After I took a shower, I went to bed.