A colon should follow a dependent clause when the dependent clause comes first in a sentence.

Explanation:

A comma should follow a dependent clause when the dependent clause comes first in a sentence. A dependent clause is the clause which cannot stand alone in its meaning on the other hand independent clause refers to the phrase which can stand alone, though both have a subject and a verb.

you didn't finish the sentence , how am i gonna you if you didn't finish the sentence

you need to add the passage to the question.