"Will you say what I told you to the teacher?"
Translation:את תאמרי את מה שאמרתי לךְ למורָה?
They are different words. אַתְּ - at - you (feminine singular). אֶת - marks a definite direct object.
if you notice the given answer it says "את תאמרי את..." which sounds like "at tomri et", the first את (pronounced "at") is the feminine singular "you" as almog said, and the second את (pronounced "et") points at the definite direct object, so the hebrew sentence translates to "you will say what i told you to the the teacher?" which also works in english.
In English, the first two words are reversed when used as a question; it would be, "Will you say what I told you to the teacher?"