The answer would be "Nine students each make 2 models of Mars and its moons. How many models did they make in total?" Since the answer is 18 and there are 9 students (and also since 18 can be divided into 9), you can divide 18 and 9 to get 2. This makes sense because if each student makes 2 models (as stated), there'd be a total of 18 models (as stated in the question you gave). Hope this helped!