Final answer:
The subject of the sentence 'The advertisement was a want-ad about cooks' is 'advertisement.' The subject of the sentence 'My mother gave Justin the advertisement' is 'mother.'
Step-by-step explanation:
In the sentence 'The advertisement was a want-ad about cooks,' the word 'advertisement' is the subject.
In the sentence 'My mother gave Justin the advertisement,' the word 'mother' is the subject.
In the sentence 'My mother gave Justin the advertisement,' the word 'advertisement' is the direct object.
In the sentence 'My mother gave Justin the advertisement,' the word 'Justin' is the indirect object.