Questions & Answers about He löysivät halvan rivitalon netistä.
Why is it netistä (from the internet) instead of netissä or netillä (on the internet)?
This is a special rule for the verb löytää (to find). In English, you find things in or on a place, but in Finnish, you find things out of a place. Because of this, löytää always requires a "from" case: either the elative (-sta/-stä) or the ablative (-lta/-ltä). Since you would normally say netissä for "on the internet", it becomes netistä with this verb.
Why are halvan and rivitalon ending in -n rather than being in the partitive case?
The -n ending here marks the accusative case (which looks exactly like the genitive case). It is used because the action of finding is complete and the object is a single, whole thing. If the action were ongoing or incomplete, like "They were looking for a cheap house" (He etsivät halpaa rivitaloa), you would use the partitive case instead.
Where does the s in löysivät come from if the dictionary form is löytää?
When forming the past tense, the marker -i- is added to the stem. For many verbs ending in -tää or -taa (like löytää, tietää, and lentää), the t changes to an s before the past tense i. The stem löytä- becomes löysi-, and then we add the "they" ending -vät.