Accusative case seems simple for singular nouns, but how would a noun (like сорочка) be pluralized in accusative?
Plural would be «Ми шука́ємо соро́чки». For inanimate nouns, plural accusative is always the same as plural nominative. For animate, plural accusative is always the same as plural genitive.
Oops! I realized that I should have used the formal ваш in my reply. I'm still getting used to that because in English we just have one form. Sorry about that.
I'm OK with «ти». :) In some environments, «ти» is the default. For example in the universities many students use «ти» when speaking to other students, even if they don't know each other, (but not to professors) — and Duolingo can be a compared to a virtual university. :)
But you should have used «твою́ ві́дповідь» or «Ва́шу ві́дповідь», because «ві́дповідь» is feminine.
Thanks again! I hope you don't mind one more question. I'm still learning about Ukrainian cases so why are the correct pronouns твою вашу? Are they vocative case?
No, they're not vocative, they're accusative. The pronoun «за» is used with accusative case when it means 'for', so «твою́/ва́шу відпові́дь» is accusative.
You could use vocative case for «мій друг», because this is a form of address. Vocative would be «мій дру́же». However, nominative works here too.
I think its correct to write СОРОЧКИ too. Ми шукаємо сорочку. Ми шукаємо сорочки.