Find the mistake and correct it

Find the mistake and correct it:
1) She meets an old friend at a dinner party last weekend
2)There are a big traffic jam on the road to the downtown
3) The trachers had a meeting at 6 o clock on the afternoon
4)We have a smoke detector on the ceiling in each classroms 
5. Schools in America are closed at Thanksgiving Day and the day after 
6.we can find out about schools in the past by looking to evidence