2. Choisir can be conjugated as a special -IR verb. Because of the article vous, we know that the ending of the word will be -ez. As shown through all -IR verbs, the ending of this word specifically would be -issez. Combined with the root of the word, chois, you would get the word choisissez.
3. Finir can be conjugated as a normal -IR verb. Because of the article nous, we know that the ending of the word will be -ons. As shown through all -IR verbs, the ending of this word specifically would be -issons. Combined with the root of the word, fin, you would get the word finissons.