Breakdown of Suunnittelitteko te yhdessä eilen?
te
you (plural/formal)
yhdessä
together
eilen
yesterday
suunnitella
to plan
Questions & Answers about Suunnittelitteko te yhdessä eilen?
How is the past tense form suunnittelitte built from the verb suunnitella?
Suunnitella (to plan) is a Type 3 verb. To make it past tense, we take the strong consonant stem (suunnittel-), add the past tense marker -i-, and finally attach the personal ending -tte (for "you" plural). Notice the consonant gradation: the infinitive has a single weak t, but the stem used for the past tense takes the strong tt.
What is the -ko at the end of suunnittelitteko?
It is the question particle. To turn the statement suunnittelitte (you planned) into a yes/no question, you attach -ko to the verb and move that verb to the very front of the sentence.
Do we really need the word te (you, plural) here?
No, it's grammatically optional! The verb ending -tte already makes it perfectly clear that the subject is "you" (plural). However, including te is very common in everyday speech and can add a little bit of natural emphasis.
How does the word yhdessä mean "together"?
Yhdessä is the standard word for "together", but it literally translates to "in one". It is formed by taking the stem of the number yksi (one) and adding the inessive ("in") ending -ssä.