Here are the required transformations from direct to reported speech for the sentences you've provided:

50. I asked Hoa if her sister was good at English.

51. My mother asked if I could cook that fish for her.

52. The teacher asked his students if they didn’t know how to behave in lessons.

53. Helen wondered to herself if she was doing the right thing.

54. Yen asked me if the Statue of Liberty was in New York.

55. I asked her if she enjoyed her English class.

56. I asked my new classmate if he/she visited the Taj Mahal in India.

57. Our friend asked if we could go to the concert with them that night.

58. She asked me if I was hungry.

59. The man asked her if she could play the guitar.

60. Thu’s mother asked her if she was willing to help her friends then.

Feel free to ask if you need further assistance!