I don't know if this is exact right physiology, but the logic makes sense in my head and I am able to get a point on this question.
To understand preload, lets talk about the afterload first, which this question is hitting at. Afterload is the amount of blood present in the ventricle after ejection. In a case of mitral regurgitation (the differential you come to with the description in the stem), your having a problem during systole (during ejection), where blood is squirting back from left ventricle to the left atrium. The normal physiology in systole is the mitral valve is closed and the aortic valve is open to squeeze blood into the aorta and deliver it to the arterial system. But that's not the case here, it's going in the wrong direction. So to minimize the amount of blood that squirts backwards, we would want to decrease the afterload.
When they are asking the question, "which of the following would increase the ratio of forward flow volume to regurgitation flow volume in this patient?", they are asking what would make this value higher, which is just increasing the numerator (forward flow) or decreasing the dominator (regurgitant flow). So, we could either decrease the regurgitant flow (afterload) -or- we could increase the numerator, which is forward flow. Forward flow is just your preload, or amount of blood present in the ventricle before ejection.