Translation:Bob is an important teacher and Carrie is an important teacher.
Besides Duolingo not having taught the duel and plural forms yet, Duolingo is just now teaching the difference between male and female endings. That's why they are writing the sentence this way, so students can see "important teacher" written, and hear it pronounced, in the masculine and feminine forms together in the same sentence so that they can be easily compared and contrasted.
I agree with mayateacher no native English speaker would repeat 'important teacher' in the above sentence, but I see that there is a distinction in Arabic in that Bob and Carrie are male and female. It is not necessary to make that distinction in English, so Bob and Carrie are important teachers should be accepted as being correct.