Теория:

Study some information about negative sentences and questions with 'can/could'.
 
Для построения отрицательного предложения с can (could) необходимо использовать следующий порядок слов:
subject \(+\) can (could) \(+\) not \(+\) Verb in the \(1\)st form (without 'to') \(+\) other parts of the sentence.
Также можно использовать сокращения отрицательных форм:
 
cannot \(=\) can't
 
(отрицание с can пишется слитно);
 
could not \(=\) couldn't.
  
We couldn't (could not) find a place to sit.
  
They can't (cannot) solve this problem now.
  
Для построения общего и специального вопросов используйте следующий порядок слов.
  
General question
Can (Could) \(+\) subject \(+\) Verb in the \(1\)st form (without 'to') \(+\) other parts of the sentence?
Special question
Question word (when, how, what....) \(+\) can (could) \(+\) subject \(+\) Verb in the \(1\)st form (without 'to') \(+\) other parts of the sentence?
Can you help me?
  
Could you work when you were \(18\)?
  
student-849822_640.png
Рис. \(1\). Working  
 
What can I do for you?
  
How could he help you in that situation?
Источники:
Рис. 1. Working , 2015, https://pixabay.com/images/id-849822/ Pixabay License CC0 Free for commercial use No attribution required