How many words of memory map to the same cache entry? I am going over some practice questions for the Major field exam and it asks: 

A processor with a word-addressable memory has a two-way set-associative cache. A cache line is one word, so a cache entry contains a set of two words. If there are  M  words of memory and C cache entries, how many words of memory map to the same cache entry?

I am not sure how to even approach this problem since I am not too familiar with computer organization. Any help would be appreciated. Thanks!
The correct answer is M/C. This question is on the Computer science Major Field Assessment Test. https://www.ets.org/Media/Tests/MFT/pdf/mft_samp_questions_compsci.pdf