15. They started talking about their future plan 2 hours ago.
=> They have been talking about their future plan for 2 hours.
16. I started writing this letter 2 hours ago.
=> I have been writing this letter for 2 hours.
17. The last time she had a swim was 5 years ago.
=> She hasn't had a swim for 5 years.
18. She hasn't had a swim since she was 15 years old.
=> The last time she had a swim was when she was 15 years old.
19. I have taken part in this English-speaking club since last month.
=> I began taking part in this English-speaking club last month.
20. Helen has read that book for a few days.
=> Helen began reading that book a few days ago.
21. Jack last had breakfast at that restaurant when he was ten.
=> Jack hasn't had breakfast at that restaurant since he was ten.
22. It's three weeks since they last had a family gathering
. => They have not had a family gathering for three weeks.
23. It's six months since we last went hiking together.
=> We have not gone hiking together for six months.
24. She started learning French last year.
=> She has been learning French since last year.
25. She has played the piano for three years.
=> She began playing the piano three years ago.
26. My mom hasn't planted trees in the garden for 3 months.
=> My mom stopped planting trees in the garden 3 months ago.
27. Kate and her husband began teaching at that school in 1998.
=> Kate and her husband have been teaching at that school since 1998.
28. She has not drunk coffee since she was sick last week.
=> She stopped drinking coffee last week.
29. The boys have played football since 2 o'clock.
=> The boy began playing football at 2 o'clock.
30. Jack hasn't had breakfast at that restaurant last year.
=> This sentence is already in the correct tense. It is in the present perfect tense, indicating an action that started in the past and continues to the present or has an effect on the present.