5. Mai used to go to school on foot when she was in primary school 

6. There are often traffic jams in the rush hour in the city center

7. People in the past didn't use to worry about traffic congestion

8. It's compulsory to wear a helmet when riding a motorbike in Viet Nam        

`~rai~`

$\begin{array}{I}\text{5.Mai used to go to school on foot when she was in primary school.}\\\text{6.There is often traffic jams in the rush hour in the city center.}\\\text{7.People didn't use to worry about the traffic congestion in the past.}\\\text{8.It is compulsory to wear a helmet when riding a motorbike in Vietnam.}\end{array}$