A few things to remember before you do this exercise:

• Unlike "ago", the German equivalent "vor" comes before the unit of time.

• After the  preposition "vor" the accusative case is used to indicate movement to a place (i.e. you can ask “where to?”), the dative case is used to indicate location (i.e. you can ask "where?") or time (i.e. you can ask "when?"), i.e. you will always need the dative case after "vor" when it is meant to translate "ago".

• Nouns in dative plural add an "n" if they do not already end in "n" or "s": 1 Jahr, 2 Jahre, vor 2 Jahren, but 1 Minute, 2 Minuten, vor 2 Minuten

• The second element in a main clause is always the conjugated verb.