Перевидите в косвенную речь: 1) He asked, "We have forgotten to take the ball". 2) She said, "I will be very glad to see you" 3) Alec asked me, "Have you ever been to National Gallery?" 4) The teacher said, "Open your books and begin reading the new text." 5) The girl asked, "What is the price of this dress?" 6) Nellie said, "Yersterday I went to see Paul, but he was not at home." 7) "Why do you help her?" said Alec to us.

He asked, "We have forgotten to take the ball".
→ He said that they had forgotten to take the ball.
(В косвенной речи have forgotten → had forgotten, а we обычно заменяется на they, потому что говорящий пересказывает чужие слова.)

She said, "I will be very glad to see you".
→ She said that she would be very glad to see me.
(will → would, I → she, you → me — если пересказ идёт от лица того, кому сказали.)

Alec asked me, "Have you ever been to the National Gallery?"
→ Alec asked me if I had ever been to the National Gallery.
(Общий вопрос: Have you…? → if/whether…, порядок слов прямой, have been → had been.)

The teacher said, "Open your books and begin reading the new text."
→ The teacher told us to open our books and begin reading the new text.
(Повелительное наклонение: said → told, структура to + infinitive, your → our / the pupils’ по смыслу.)

The girl asked, "What is the price of this dress?"
→ The girl asked what the price of that dress was.
(Специальный вопрос: слово what сохраняется, порядок слов прямой, is → was, this → that.)

Nellie said, "Yesterday I went to see Paul, but he was not at home."
→ Nellie said that the day before she had gone to see Paul, but he had not been at home.
(yesterday → the day before, went → had gone, was not → had not been.)

"Why do you help her?" said Alec to us.
→ Alec asked us why we helped her.
(Специальный вопрос: why сохраняется, порядок слов прямой, do you help → we helped, you → we.)