Since identifying the marketing challenge or the problem facing the company in a case study is so crucial to your analysis, let's take some time here...

Since identifying the marketing challenge or the problem facing the company in a case study is so crucial to your analysis, let's take some time here to proffer our ideas on what we think is the main challenge facing McDonalds.

Generally, you can find the challenge either in the first couple of paragraphs or the last paragraph. Sometimes it jumps out at you and sometimes you have to look hard for it. 

Sometimes it is spelled out and sometimes it is a comment by a company executive.