맛있는 is verbal modifier (notice how it's attached to a verb not a noun). This means it describes the noun that follows, i.e. 맛있는 소고기 means "delicious beef" or "tasty beef". I suggest reviewing the tips and notes for the Modifiers 1 skill (accessible from the mobile/desktop website not the mobile app).
⭐ Click here to view this same post in your browser if the text below isn’t organized into a table layout; tables don’t seem to display correctly on Duolingo in Android from my experience. I might just switch back to bulleted lists for future posts.
|Part of Sentence||Decomposition|
|맛있는||맛있다 (to be tasty) + 는 (present attributive ending)|
|소고기는||소 (cow) + 고기 (meat) + 는 (topic marker)|
|많이||많이 (very) ← 만ᄒᆞ다 (to be a lot) + 이 (adverbial ending)|
|비싸요||비싸다 (to be expensive) + ㅏ요 (polite ending)|
(맛있는 소고기는) (많이 비싸요).