Let n be a positive integer. Define Zn = {0, 1, 2, ..., n-1}. Let a, b ∈ Zn. Show that there exists a unique element of c of Zn, such that n divides ab-c.

OK. This is the question translated in words. Let n be a positive integer. Define Z sub n to be equal to the set {0, 1, 2, ..., n-1}. Let a, b be elements of set Z sub n. Show that there exists a unique element of c of Z sub n, such that n divides (a times b) minus c.

This question I am beyond lost, especially since our prof just gave us this problem with no examples to compare it to. I feel like you have to take some arbitrary element and somehow manipulate via proof to show that n divides ab-c.