Ian Stewart wrote:You don't need to know what a "dividend" is on the GMAT, and if this were a real GMAT question it would declare that all of the numbers are positive.

In this question, we're dividing z by x, and getting a quotient of y and a remainder of r. So z = xy + r

Using either Statement alone, we really have no information that would let us compare x and y, so the answer is C or E.

Using both Statements together, we have 151 = xy + 11, so 140 = xy. It might seem this is not sufficient, but we know one more thing: we get a remainder of 11 when we divide z by x. That's only possible if we're dividing by something larger than 11. So x > 11, and since x and y are integers that multiply to 140, x is at least 14, and y is at most 10, and x > y. So the answer is C.