Is 먹어요 informal, and 먹습니다 formal?
먹습니다 is max politeness, 먹어요 is standard politeness, and 먹어 is casual.
More like low formal and high formal respectively. 먹어 is informal.
Can Duolingo indicate which politeness level they want, maybe in brackets?
Sometimes it's polite, sometimes formal. Drives me nuts.
I think both ways are formal