The question requires us to explain how a conversion factor must be used in a dimensional analysis expression.
We can say that a conversion factor is a fraction that we use to convert one unit of measure to another (as long as they measure the same quantity), and it conveys the relationship between these units of measure.
When using a conversion factor in a dimensional analysis process, we need to consider it as a "constant" that multiplies the expression of the dimensional analysis (and always with units that refer to the same measurement). We can't use it as a number in an addition or subctration, for example, or use a conversion factor of volume with an unit of distance.