6=5+1,6=1+5,6=2+4;6=4+2

21. Maria (not/play) has not played the guitar since she (graduate) graduated from high school.

22. They (always/ walk) always walked along the beach in the afternoon when they (be)were  on their holiday in Greece last summer.

23. My mother asked me if I (go) went to the museum with my friends the day before. And I said, “Yes, Mom. We (have) had a lot of fun.”

36.Timmy has not seen Tiana since she moved to New York.

37.The bag was too heavy for her to carry.

38. Homework should be submited before next Sunday.

39.You don't have to go  out at this time at night.

40. It takes Rosie nearly 3 hours to clean the house.

=>24,3-y:16 = 30,34+3,4

=>24,3-y:16 = 33,74

=>y:16=24,3-33,74

=>y:16=-9,44

=>y= -9,44 x 16

=>y= -151,04

Vậy y = -151,04