Here x and y are two numbers whose sum is 10 and product is 21. A useful HSC-level trick is to think of them as roots of the quadratic equation t² - (10)t + (21) = 0. After factoring or solving that quadratic, we get the two possible numbers. Since the question asks for ordered pairs, the order matters: if the two numbers are different, both (first, second) and (second, first) are valid. Checking the selected pair(s), each one has sum 10 and product 21. Therefore the correct answer choices are (7, 3), (3, 7).